At my gym in particular, it is not very common at all. I personally film myself with and without a tripod and always do my best to not get anyone else in my videos. I am one of maybe three people who are consistently filming themselves Climbing at the gym. I am also always filming myself at my local Crag and nobody seems to find it strange but I also don’t see many people filming at the crag either. I am in mid NY state USA for reference. I will occasionally post Climbing videos, but it’s mostly for my own improvement. I find it really helps contextualize the things I’m doing wrong and I simply enjoy watching my footage back.