Apple Watch Series 6 - latest WatchOS

Hello! My Apple Watch 6, with the latest update installed, started to behave strangely.

The screen went black but the watch is still connected to my iphone, vibrates, and charges. For some reason, the only thing I can think off, was using it shortly in a swimming pool (that should not be impacting...).

After some hours, it started to work again just to go black shortly after.

Note that if I force restart it, I can see the Apple logo appearing, so to me, it does not seem to be an hardware issue. I also know that Watch 6 build by end of 2020 have an issue with going permanently black.

What should I check? And... should it be a recognized bug, can it be fixed for free even now by Apple?

Thank you and best regards!