apple watch does not boot up

Have you followed all these steps:

If your Apple Watch won't charge or it won't turn on - Apple Support

especially (toward the end) where it says:

Find out what to do if your Apple Watch Series 5 or Apple Watch SE is in Power Reserve and won’t charge.

If you still need help, contact Apple Support.

Hi,

Press and hold the two buttons (the larger, circular Digital Crown and the smaller oblong Side Button) simultaneously for 10 to 15 seconds. After the Apple logo appears, release the buttons and wait another few seconds. When the watch turns back on, it should work smoothly again.

Thanks and Best Regards:

Windows Club