Having trouble opening Illustrator 2021 on my iMac. Running Catalina 10.15.7.

[reobuck0]

It seems to load then just stops before the workwindow opens. Message says (Not responding) I have uninstalled illustrator and reinstalled and have the same problem. 

[marliton]

Hi. Have you tried resetting the preferences? https://helpx.adobe.com/illustrator/user-guide.html/no/illustrator/using/setting-preferences.ug.html

[Mike_Gondek]

Reset Prefs Thoroughly (Mac)

• Quit Your Adobe App (100% you must do this)
• Finder >> Go (hold down option to show hidden) >> library 
• Preferences >> Adobe  >> (Program Name) rename to (Program Name) .old
• Library- >> Caches >> com.(Program Name) rename to (Program Name) .old
• Library >> Application Support >> Adobe >> (Program Name) rename to (Program Name) .old

OOBE RESET MAC

• Quit the Creative Cloud desktop app  (100% you must do this)
• /Users/<user folder>/Library/Application Support/Adobe/OOBE
• The \Users\<user folder>\Library\ is hidden by default for macOS 10.7 and above. See Access hidden user library files | Mac OS 10.7 and later for instructions to access it.
• Delete all the files within the OOBE folder, but do not delete the folder itself.
• Restart the computer and launch the Creative Cloud desktop app again.
• Delete all the files within the OOBE folder, but do not delete the folder itself.
• Restart the computer and launch the Creative Cloud desktop app again.

If that does not resolve your issue

Reinstall App

Use the Creative Cloud Cleaner to fully remove your app & prefs then reinstall

I am running on Catalina also. Don't go to Big Sur.