my apple watch serial 5 is syncing every day for the last 2 days and it takes 4 hours to sync

I suggest you Unpair and erase your Apple Watch - Apple Support. It sounds like something got corrupted, it shouldn't be syncing like that. You also could Contact - Official Apple Support for more help. Good luck.

I have a Apple watch 3, iPhoneX, iOS 13.7, and mine does the same thing. I have paired and unpaired numerous times. nothing has helped