How to remove stubborn tile adhesive?

Link is not allowed. Check out Hilti, Festool, Makita for concrete grinders. The grinding discs listed are then for adhesive, epoxy, etc.

For the corners, it is best to use a powerful angle grinder with a 115 or 125 mm grinding disc and extraction.

Thank you all. I have also heard about the asbestos. We will definitely wear respiratory protection, as the tiles are from 1979. [...]

Respiratory protection plus a sealed disposable overall. The vacuumed dust must then of course also be properly packaged and disposed of.

The grinding wheels are probably coarser then, like this specimen, right?

I would first try with Hilti and the proper attachment. Angled wide scraper! That is exactly for this purpose.

Sanding certainly works, but it makes a lot of mess.

that is a pot for the angle grinder. You use it for the corners where the big grinder can't reach. It's not for the surface, there you'll be reduced to a file. Especially since extraction doesn't work 100% with these things.