I know ppl that breathe with mouth during sleep say they felt much better after taping their mouths so they use their nose instead. Don’t tape it shut tho lol (disclaimer
Last time at a pharmacy, I saw they selling these tapes, to my surprise, quite many brands are making these. I thought it was a niche market, but after tried it anyway, I can feel the improvement actually. (Isolated case)
I've seen chin straps (wrap something around your head), probably similar effect. I couldn't do tape, I have a beard xD