Prior to 2019.3 EAP (and possibly even 2019.2.3, I forget), these options just showed a list of changed files. Now there's a more elaborate checkboxed list with a diff on the right, which is fine, but intellij is no longer listing in red any files that were not merged properly. Everything appears under "default changelist" and the file with merge conflicts is blue like all the others.
If it makes any difference, I performed the merge command outside of intellij and am just using intellij to look at the changes.
IntelliJ IDEA 2019.3 EAP (Ultimate Edition)
Build #IU-193.2956.37, built on September 10, 2019
IntelliJ IDEA EAP User
Expiration date: October 10, 2019
Runtime version: 11.0.4+12-b462.3 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0
GC: ParNew, ConcurrentMarkSweep
Non-Bundled Plugins: FindBugs-IDEA, VisualVMLauncher, com.mnw.tabmover, com.jetbrains.upsource, luonq.ScrollFromSource, BashSupport, cz.daku.intellij.extraActions, org.turbanov.run.configuration.as.action