I don't think I've ever heard anyone complain about that, and I know a good amount of people who use Garmin watches. My own forerunner is still going strong after 5 (I think) years of use, with multiple runs a week for most of that time.
I've had my Fenix 5 Plus swapped once during warranty because of this. And the replacement's contacts started to corrode again when I sold the watch. It might not happen to all models, but some are very prone to it.
They make little ~rubber caps to cover the charging port when you're not using it. That, and make sure it's dry when you charge it to rule out galvanic nonsense.
I know someone whose garmin watch refused to charge after a few years, not sure if it was caused by sweat. Mine is starting to get wonky after a few years. I keep worrying I'll plug in some time and it will stop. anec-data is not that reliable of course.
