Apple Watch is stuck on solid apple logo, cannot connect to iPhone and can’t reboot

You tried the forced restart?

You should force-restart your Apple Watch as a last resort and only if it's not responding.

Don't force-restart your Apple Watch if you're updating watchOS. When you see the Apple logo and progress wheel, leave your watch alone and on its charger until the update has finished.

To force-restart your Apple Watch, press and hold both the side button and the Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo.

Good luck, mine also did this (series 3). Apple said it would cost a base of $159 to repair after sending it in. Seems that many of us had this problem after the update! Yet apple says there’s “no way to know” if it was their software!