My Apple Watch SE shows red battery dead flash and time nothing else and it’s stuck there

If you are seeing just the time and a red lightning bolt, then your battery needs to be charged. See this for help.If your Apple Watch won't charge or it won't turn on - Apple Support

That is power reserve mode;

To turn off power reserve mode,press and hold the side button for about 10 seconds, until you see the watch restart and the Apple logo appear.

Keep in mind that if your battery is almost completely empty, you might need to charge the watch before it will restart normally.