Just in case you and others are out of the loop here a quick summary.
Since NovelAI announced their new image generation AI and revealed that it was trained on Danbooru's database, artist became upset by this news. Mainly they don't want their pictures to be used as training material for AI and/or view Danbooru as an 'illegal reprint' site.
Despite not beeing affiliated nor endorsing NovelAI's action, these artist started to send take down requests in order to prevent the AI from learning from their pictures, unknowingly that the AI also uses other sources (like twitter and pixiv) to learn, or since they only now became aware that Danbooru exists and don't want their works uploaded here.
Other then that I guess this topic will be just a repeated of the discussion happend in topic #22205