Someone on my team figured out that by setting Layout to Default, it fixes this problem.
We don't know why. But it's a consistent fix.

Started happening from one day to another. Didn't change a thing in the whole project.
Now I can't work.

i found that when probuilder is installed and you have accidently clicked to activate the vertex, edge or face selection tool. it disables the rect transform and other tools on the top bar.
Changing probuilder back to Object Selection, fixed this for me.

The Q/A team specifically noted what versions are effected and reproduced the issue in all of them. You can simply open the project and see that the entire rect tool no longer functions. Several users have experienced the same issue. Curious how this was marked not reproduceable?

Issue started earlier this year. Sometimes goes away but then comes back. The entire Rect transform tool stops working, so you can't move object's locations or change their size using the mouse. Tried exporting and re-importing objects, removing and re-adding to scene, deleting and re-creating prefabs, no effect.