Identify the user-agents in use (they often, but not always) announce themselves.
Use crawler blocks lists, ip blocking.
Captcha helps.
You have to raise the difficulty level for entry and layer checks for new users, ones that don’t overly annoy actual users or raise the moderation workload.
Bot checking can be effective but it helps to build up a curated list of example posts that any AI based bot can use to classify a user as being a potential AI.
Welcome to the new digital era, ain’t it grand 