Mac Mini 2020 can't recover from internet how to enable boot from external usb drive?

Hi

After formatting the internal SSD I can't go into recovery mode.

So pressing Command-R lead me to recovery over internet which stuck too, my wifi is good but the earth is keeping running and finally show apple.com/support -2002F

So I want to reinstall macOS from external drive, but unfortunately that need to go into recovery mode to enable the T2 to boot from external drive.

A dead cycle...for me.

Is there any cool guys could help me solve this?

Somebody may ask me why formatted the internal SSD?

Well, that's a sad story. This afternoon my building suffered a power cut.

After the power resume my mac suddenly keep freezing when startup. The OS version is 10.15.6. Catalina seems to Verifying every app and freeze everything even Finder.

Is the power failure damaged the internal SSD? I don't know.

So I decided to restore the mac from TM to my latest usable time.

Restore success. Hardware seems OK.

But still freezing.

Then I decided to format the SSD and reinstall everything.

That's the story.

Thank you everyone! I'm trying to not omit any key information but my English is not so good, so if above is hard to understand please ask me and forgive me :)