Go to Finder, navigate your way to the file in question, then Option-click/right-click on the file in question. In the pop-up context-sensitive menu, choose the Open With command. I'll just about betcha that it isn't set to open with InDesign CC2021 as the default. If you click on that option, I'll also betcha it finally opens for you.
Now, how to fix it: in Finder, click once on the file and press the keyboard shortcut Cmd+I to open the Get Info dialog box for your file. Change the default to InDesign CC2021, then choose to make all files of this type open with InDesign CC2021 and you should be past the problem ... for InDesign documents. You'll want to do the same with InDesign templates (.indt), book (.indb), library (.indl) and InDesign interchange format (.idml) files too.