Thank you for your support. The issue is now fixed in the latest update of InDesign.
Please upgrade to the new InDesign 14.0 from your Creative Cloud Application.
If you are unable to see the update yet, click on the menu (three dots) on the top right corner of Creative cloud app and click on “Check for App Updates”.
Let us know your feedback in the comment section.
InDesign TeamNiels commented
Well I think I may have found a solution to being able to expand palettes without using the app frame:
I'd tried a bunch of solutions here but none worked (short of trashing prefs)... BUT as I was angrily banging away on the palettes wishing they would expand I grabbed the top of the palette set and dragged it away from it's locked position at the top right of the screen... and guess what? Suddenly I can expand the palettes. Joy! If I slide the palettes back up to their locked position in the upper right... bingo, they stop expanding. Then I drag them away and... expansion!
Hope it works for you folks.