@halumein Thanks so much for answering those questions for us!
With Cloud Sync disabled on your Ubisoft Connect launcher, it shouldn't ever overwrite your PC save with your PS5 save.
In regards to being disconnected, however, a Ubisoft Connect account cannot be online on two devices at once. As such, if the PS5 copy is being played by someone else, I would recommend that they create a separate Ubisoft Connect account. This has the additional benefit of being doubly sure that any cloud saves would not sync to other devices not also connected to that account. You'l...