The rocker held his first public show at WeHo's Whisky a Go Go, which was packed to the gills with folks dying to get out and catch some tunes up close and in the flesh. It's all kosher, obviously -- the state of California is open again, and masks are largely optional.

However, it's interesting to see that the majority of people here chose not to wear a face covering ... especially because we've heard it was all basically on an honor system in terms of vaccination. We've heard from people who went that there were no vaxx card checks ... so it's a little dicey. Some may have been vaccinated, others easily might not have been.

That might make you squirm a bit when you see just how huddled and close people got during the performance -- especially when Yungblud got down low to the ground level.

At this point, it appears enough people are getting vaccinated that these people felt comfortable enough to take the chance ... to which we say, rage at your own risk. Word around town is that a lot of these smaller venues aren't checking vaccine status, so ... 🤷🏽‍♂️

BTW, Machine Gun Kelly and Megan Fox were in attendance for this shindig -- they're pals with Yungblud -- and of course, they were doing their thing up in the upper deck ... making out and stuff.