Do I have to show proof of vaccination upon entering?

I would check the venue or Ticketmaster prior to attending because it can change depending on how bad the COVID levels are in that area.

Depends on artist. I'd wager, no. But a picture will work fine regardless

Deftones weeks back,they never even asked...like Eric said,depending on the artist

Depending on who’s playing and if it’s required, yes. A photo works