In the Lemmy Web UI, beneath a post or comment from a user, click the three dots and choose "Block User".
In the Jerboa Android client, tap the three dots beneath a post or comment by the user and choose "Block".
If you're using a different client, it'll depend on that client.
I'd point out, though, that @Track_Shovel doesn't just do gross-out AI art. He also submits stuff that you may (or may not) like more, like this series of Warhammer 40k images in various media:
So even if you really don't like gross-out art -- I myself am not a fan of the genre -- you might just want to downvote stuff that you don't like and upvote stuff that you do, or you could miss future stuff that he submits that's more up your alley.
Consider that you've submitted a broad range of stuff yourself: