Rests

There's nothing changed in that regard, not with any update I know if.

Check your note input mode by clicking the fancy N under the new score icon.

Can you input a note?

See:
https://musescore.org/en/handbook/note-input-modes
especially:
https://musescore.org/en/handbook/note-input-modes#steptime
Which is the method of note entry that MuseScore has had from the beginning.

To enter a rest, press 0 (zero). See:
https://musescore.org/en/handbook/note-input#enter-pitch

Regards.