there's been nudity on tumblr the whole time that presumably just never got reported, but I definitely have seen an uptick since the policy change
in the past it's always been, from the corner I ended up finding, like 70% nude art modeling and 30% ppl who just happen to be nude taking selfies and such. probably bc I was self-selecting content I searched but I didn't see almost any porn or porn-adjacent stuff, so you definitely could avoid it. hard to say what it's going to be like until the dust of the new change has had a chance to settle tho
tumblr's lack of a nudity policy back in the day did actually help me a lot with feeling less alienated w the world. I think having to have something labeled Mature is gonna pull away from that, but also I guess we'll see