Based on https://bsky.social/about/support/tos#user-content , I would answer yes. While it's not expressly called out (permitted or forbidden), my reading of the above would indicate that it's not forbidden per se, and probably permitted ("Modify or otherwise utilize User Content in any media. This includes reproducing, preparing derivative works, distributing, performing, and displaying your User Content."). I believe training an LLM falls under "utilize" and "preparing derivative works".

That's about your user content, not others'.