Can't open projects after updating to 2021.3

The issue is caused by the Scala plug-in and is being investigated at SCL-19741.

Workarounds:

• Switch to the release Scala plug-in version (only nightly build 2021.3.503 is affected, 2021.3.504 nightly and 2021.3.14 release builds already contain the fix)
• Disable Scala plug-in
• Downgrade to 2021.2.3 release here or using the Toolbox App
• Downgrade to 2021.3 RC build which is not affected:
  https://download.jetbrains.com/idea/ideaIU-213.5744.202.exe
  https://download.jetbrains.com/idea/ideaIU-213.5744.202.tar.gz
  https://download.jetbrains.com/idea/ideaIU-213.5744.202.dmg

We apologize for the inconvenience caused. The issue has the highest priority and will be fixed soon.

You are affected by this problem if you see the following in idea.log:

2021-11-30 19:00:57,070 [ 12154] ERROR - nsions.impl.ExtensionPointImpl - Cannot create extension (class=org.jetbrains.plugins.scala.lang.formatting.settings.ScalaLanguageCodeStyleSettingsProvider) [Plugin: org.intellij.scala] 
com.intellij.diagnostic.PluginException: Cannot create extension (class=org.jetbrains.plugins.scala.lang.formatting.settings.ScalaLanguageCodeStyleSettingsProvider) [Plugin: org.intellij.scala]
at com.intellij.serviceContainer.ComponentManagerImpl.createError(ComponentManagerImpl.kt:931)
at com.intellij.openapi.extensions.impl.XmlExtensionAdapter.createInstance(XmlExtensionAdapter.java:88)
at com.intellij.openapi.extensions.impl.ExtensionPointImpl.processAdapter(ExtensionPointImpl.java:489)
at com.intellij.openapi.extensions.impl.ExtensionPointImpl.processAdapters(ExtensionPointImpl.java:437)
at com.intellij.openapi.extensions.impl.ExtensionPointImpl.computeExtensionList(ExtensionPointImpl.java:249)
at com.intellij.openapi.extensions.impl.ExtensionPointImpl.getExtensionList(ExtensionPointImpl.java:243)
at com.intellij.openapi.extensions.ExtensionPointName.getExtensionList(ExtensionPointName.java:39)
at com.intellij.psi.codeStyle.LanguageCodeStyleSettingsProvider.calcSettingPagesProviders(LanguageCodeStyleSettingsProvider.java:385)
at com.intellij.psi.codeStyle.LanguageCodeStyleSettingsProvider.lambda$getSettingsPagesProviders$2(LanguageCodeStyleSettingsProvider.java:379)
at java.base/java.util.concurrent.atomic.AtomicReference.updateAndGet(AtomicReference.java:209)
at com.intellij.psi.codeStyle.LanguageCodeStyleSettingsProvider.getSettingsPagesProviders(LanguageCodeStyleSettingsProvider.java:379)
at com.intellij.psi.codeStyle.CodeStyleSettingsServiceImpl.getCustomCodeStyleSettingsFactories(CodeStyleSettingsServiceImpl.java:64)
at com.intellij.psi.codeStyle.CustomCodeStyleSettingsManager.initCustomSettings(CustomCodeStyleSettingsManager.java:25)
at com.intellij.psi.codeStyle.CodeStyleSettings.<init>(CodeStyleSettings.java:101)
at com.intellij.psi.codeStyle.CodeStyleSettingsManager.createSettings(CodeStyleSettingsManager.java:52)
at com.intellij.psi.codeStyle.ProjectCodeStyleSettingsManager.setMainProjectCodeStyle(ProjectCodeStyleSettingsManager.java:79)
at com.intellij.psi.codeStyle.ProjectCodeStyleSettingsManager.<init>(ProjectCodeStyleSettingsManager.java:37)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at com.intellij.serviceContainer.ConstructorInjectionKt.instantiateUsingPicoContainer(constructorInjection.kt:52)
at com.intellij.serviceContainer.ComponentManagerImpl.instantiateClassWithConstructorInjection(ComponentManagerImpl.kt:876)
at com.intellij.serviceContainer.ServiceComponentAdapter.createAndInitialize(ServiceComponentAdapter.kt:47)
at com.intellij.serviceContainer.ServiceComponentAdapter.doCreateInstance(ServiceComponentAdapter.kt:37)
at com.intellij.serviceContainer.BaseComponentAdapter.getInstanceUncached(BaseComponentAdapter.kt:113)
at com.intellij.serviceContainer.BaseComponentAdapter.getInstance(BaseComponentAdapter.kt:67)
at com.intellij.serviceContainer.BaseComponentAdapter.getInstance$default(BaseComponentAdapter.kt:60)
at com.intellij.serviceContainer.ComponentManagerImpl.instantiateService(ComponentManagerImpl.kt:1044)
at com.intellij.serviceContainer.ComponentManagerImpl$preloadServices$1.invoke(ComponentManagerImpl.kt:1016)
at com.intellij.serviceContainer.ComponentManagerImpl$preloadServices$1.run(ComponentManagerImpl.kt:56)
at java.base/java.util.concurrent.ForkJoinTask$AdaptedRunnableAction.exec(ForkJoinTask.java:1407)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinTask.doJoin(ForkJoinTask.java:396)
at java.base/java.util.concurrent.ForkJoinTask.invokeAll(ForkJoinTask.java:853)
at com.intellij.serviceContainer.ComponentManagerImpl$preloadServices$2.run(ComponentManagerImpl.kt:1031)
at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1736)
at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1728)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Caused by: com.intellij.diagnostic.PluginException: Cannot create class org.jetbrains.plugins.scala.lang.formatting.settings.ScalaLanguageCodeStyleSettingsProvider (classloader=PluginClassLoader(plugin=PluginDescriptor(name=Scala, id=org.intellij.scala, descriptorPath=plugin.xml, path=~/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-1/213.5744.223/IntelliJ IDEA.app.plugins/Scala, version=2021.3.503, package=null, isBundled=false), packagePrefix=null, instanceId=320, state=active))
at com.intellij.serviceContainer.ComponentManagerImpl.instantiateClass(ComponentManagerImpl.kt:869)
at com.intellij.openapi.extensions.impl.XmlExtensionAdapter.instantiateClass(XmlExtensionAdapter.java:99)
at com.intellij.openapi.extensions.impl.XmlExtensionAdapter$SimpleConstructorInjectionAdapter.instantiateClass(XmlExtensionAdapter.java:116)
at com.intellij.openapi.extensions.impl.XmlExtensionAdapter.createInstance(XmlExtensionAdapter.java:66)
... 41 more
Caused by: java.lang.IllegalAccessException: no such constructor: org.jetbrains.plugins.scala.lang.formatting.settings.ScalaLanguageCodeStyleSettingsProvider.<init>()void/newInvokeSpecial
at java.base/java.lang.invoke.MemberName.makeAccessException(MemberName.java:959)
at java.base/java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1101)
at java.base/java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:2030)
at java.base/java.lang.invoke.MethodHandles$Lookup.findConstructor(MethodHandles.java:1264)
at com.intellij.serviceContainer.ComponentManagerImpl.instantiateClass(ComponentManagerImpl.kt:830)
... 44 more
Caused by: java.lang.NoClassDefFoundError: com/intellij/application/options/IndentOptionsEditorBase
at java.base/java.lang.invoke.MethodHandleNatives.resolve(Native Method)
at java.base/java.lang.invoke.MemberName$Factory.resolve(MemberName.java:1070)
at java.base/java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1098)
... 47 more
Caused by: java.lang.ClassNotFoundException: com.intellij.application.options.IndentOptionsEditorBase PluginClassLoader(plugin=PluginDescriptor(name=Scala, id=org.intellij.scala, descriptorPath=plugin.xml, path=~/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-1/213.5744.223/IntelliJ IDEA.app.plugins/Scala, version=2021.3.503, package=null, isBundled=false), packagePrefix=null, instanceId=320, state=active)
at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.java:235)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
... 50 more