This sounds crazy but just found this video on YouTube and every person said it worked for them in the comments....by the 6th step something will work
Hard reset with both buttons pressed for 15 seconds
Go in your watch app on your phone and change the "face" on your watch - doesn't matter which one. Put back on charger and hold crown and side button until apple logo appears...if that doesn't work
Take watch off charger tap side button 15 times really fast then crown immediately after 15 times. Put back on charger, hold side buttons again to force start
Take off charger, rub your watch face really hard with your thumbs all over, really press hard for like 10-12 seconds. Turn over and do the same to the back. Tap the side buttons again a bunch. If still black...
Set watch down flat and tap watch face a bunch, pretty hard with finger all over, flip over and repeat on backside. Tap all over
If none of that worked put in freezer for 15-20 minutes. Then put on charger (50% of people said this is what worked for them)
If still nothing start at step 1 again.
Good luck!!
https://youtu.be/QYP5icStMV4?si=CX9vgfk2BdMkt-at