Why reboot your whole SteamOS handheld to desktop when you can visit the desktop from inside the gaming mode? Nested Desktop does have limitations (no file management, no Steam-within-Steam) but gosh are there times this’d come in handy. Jacob at XDA calls it “the best Steam Deck feature you aren’t using”.
Setup: In desktop mode, tap Steam logo on taskbar > scroll down to Lost and Found > Right-click “Nested Desktop” > “Add to Steam.”