Seems like this Home Connect stuff does support local only/no cloud mode[0]. I recently discovered my parent's kitchen hardware is all Bosch with Home Connect and was afraid I had to run it through their cloud. But there seems to be some decent effort done in getting it to work with Home Assistant[1].
[0] https://trmm.net/homeconnect/ [1] https://github.com/hcpy2-0/hcpy