Question about Garmin fenix 6 Pro

In principle, yes, but you have to rinse the watch very well with fresh water after swimming. In various forums you can read about people who have had problems because the contacts at the back are corroded. The watch has no problems with water per se.

Yes, I don't think that should be a problem, and I also wear the watch when I go into the sea. After contact with salt water, rinse the watch well with fresh water.