The roborock S5 and older models can easily be rooted, and you can install alternative open source firmware [0], newer models still require hardware disassembly in order to flash the firmware, so it's not quite user friendly yet [1]
For newer versions you can however extract the API token from the app, and use it to control the vacuum without internet access and block its external internet access, since the vacuum uses a known protocol. [2]
[0] https://github.com/Hypfer/Valetudo
[1] https://github.com/dgiese/dustcloud/issues/213#issuecomment-...