I also have questions about this:
Case study:
I put on the chest strap, which I have previously connected to the smartwatch, for outdoor football and the watch remains in the changing room.

Will all the data (distance, GPS, heart rate, etc.) be recorded during football?
Will this data then be transmitted to the watch as soon as the smartwatch is reconnected?

Yes, simply connect the app to the belt. The data is updated after the sports session