I'm not sure about the flag :D but I've had pretty good results with always making sure to flag every artist in AI suggestions with "don't play". You have to visit the artist profile pages to do it though, so it remains a cat and mouse game, but I think that as long as they don't prevent it by force, doing this tends to improve the AI suggestions (of non-AI music).

Similar to YouTube slop.

If that would stop working, I'd cancel Spotify again.

Speaking of YouTube slop, I think Spotify has had its own system of preferring cheap muzak from labels they support since before GenAI music even took off, I think. Example label: Firefly entertainment (IIRC)