Some datacentres do in fact recover the heat for things like municipal heating. It's tricky though because being near population centres that can use the heat is often (not always) inversely related to things that are good for datacentres like cheap land, power and lack of neighbours to moan about things like construction and cooling system noise.
There was also a startup selling/renting bitcoin miners that doubled as electrical heaters.
The problem is that computers are fundamentally resistors, so at most you can get 100% of the energy back as heat. But a heat pump can give you 2-4 times the energy back. So your AI work (or bitcoin mining) plus the capital outlay of the expensive computers has to be worth the difference.
There was also a startup selling/renting bitcoin miners that doubled as electrical heaters.
The problem is that computers are fundamentally resistors, so at most you can get 100% of the energy back as heat. But a heat pump can give you 2-4 times the energy back. So your AI work (or bitcoin mining) plus the capital outlay of the expensive computers has to be worth the difference.