Unable to install “IntelliJ IDEA CE”.

Where do you get this error? 
May you show a screenshot? 

I am getting the same error. I can not install IntelliJ Ultimate (trial) intelliJ-ideaIU-2021.1.dmg

Mac OS X 11.2.3

java -version
openjdk version "16" 2021-03-16
OpenJDK Runtime Environment (build 16+36-2231)
OpenJDK 64-Bit Server VM (build 16+36-2231, mixed mode, sharing)

Get Info for /Applications/IntelliJ IDEA.app (while the below error dialog is displayed)

Error Dialog

Do you have an antivirus installed on your mac? 

Try reinstalling IDE via ToolBox: https://www.jetbrains.com/toolbox-app/

I have tried the install via the Toolbox, same result.

Yes, I have Trend Micro Antivirus on my Mac

 I have Trend Micro Antivirus on my Mac

Please disable it, most probably it prevents IDE from start. 

Trend Micro A/V disabled and still the same error. Note that I can install other apps without this error. I just installed Charles Proxy via .dmg file, no issues.

Also note I had previously installed IntelliJ but was having issues on start, so I uninstalled and now I am attempting to re-install.

Try to start the IDE from command line: https://intellij-support.jetbrains.com/hc/en-us/articles/360011901879-How-to-start-IDE-from-the-command-line 

What is the output? 

I can't even install the app, so I can't launch the IDE either

I did mount the .dmg from the command line and attempted to copy "IntelliJ IDEA.app" to /Applications. _Most_ of the files were copied but 12 were not, each failed copy statement had the error message "Operation not permitted"

I have Full Disk Access assigned to the Terminal.app

I finally got IntelliJ installed via Toolbox after shutting down Trend A/V with

   sudo launchctl unload /Library/LaunchDaemons/com.trendmicro.* /Library/LaunchAgents/com.trendmicro.*

Thank you for your help!