Hello, with Add/mesh/plane etc an initial input menu appears at the bottom left for size, segments radius… But it is darker than usual and nothing can be entered, e.g. for the cylinder nothing for vertices, radius, depth…it just disappears when I click on it. 2.9.1, (Object Mode) It still worked under edit mode, but now it doesn’t work there either. Not in any file, not even the old ones. Thank you for considering.
If this happens for new files and old files you could try disable any recent installed addon and/or reset to factory settings.
Enable Global Undo in User Preferences -> System.
Many thanks Rigoletto, that way I learned that the mistake occured with the “add mesh extra objects” add-on enabled. But it is useful. Is it an incompability- bug? Because with “Enable Global Undo in User Preferences -> System” it works…
Many thanks Stan-Pancakes, that solved the problem!