Valetudo. I haven’t had personal experience using it (due to an unsupported model of NAND memory chip), but I’ve heard good words: https://valetudo.cloud/

That said, I did some research last year before buying my first robot vacuum. I wasn’t able to find a project - Valetudo included - that would support the bigger, fancier robots made by Roborock etc. If you’re looking to decloud a recent model, I don’t have a good answer.

I have a Xiaomi one, and that also connects to the cloud if you wanna use the smartphone app, but you can just not connect it to the internet, set it down, push the button and it does its thing

Honestly, the dumber the better. The old 0 smarts Vileda VR102 still outperforms most of the expensive sensor laden connected units I've encoutered. Sadly no longer available (except online at 4x their original cost).