Gordon is correct, you cannot directly drag and drop a single note from one staff to another in MuseScore 4.
However, you can achieve a similar effect for cross-staff notation by using the following method:
1) Enter the notation in one staff first.
2) Select the note or notes that you wish to move to the other staff. Use the keyboard shortcut Ctrl + Shift + ↓ (Windows) or Cmd + Shift + ↓ (Mac) to move the selected notes down to the staff below. If you want to move them to the staff above, use ↑ instead of ↓.

I checked, when I use my keyboard to enter an Am triad, on the bass cleff, it defaults to the image you show. So then you just need to use the method shown to move the selected notes to the Treble Cleff.

Tell your buddy to open Chat GPT when he has any questions like this in musescore. The entire manual is over there.

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, Motu Audio Express 6x6 - My SoundCloud (Tip: No need to create a SC account to hear music - just hit ESC ).