Fix for this issue is now available in the latest update of InDesign 2020.
In the Creative Cloud Desktop application, click on the Updates section on the left. You should be able to see the Update available for InDesign. Please update your InDesign application to this version to try out the fix.
Let us know in the comments section if you face any problem with the updation process.
Adobe InDesign TeamAnonymous commented
You're not alone. I'm having that problem too since my last Adobe update. I can use CMD-Arrow to navigate around text just fine in text blocks, but inside tables it's stopped working. It's sooooo annoying! I need it back now please!