Erase computer when it won’t turn on

Do you recall if a password screen appeared prior to the appearance of the Apple "progress bar" upon startup?

Excerpted from Use FileVault to encrypt the startup disk on your Mac:

"When FileVault setup is complete and you restart your Mac, you will use your account password to unlock your disk and allow your Mac to finish starting up."

Encrypt Mac data with FileVault - Apple Support

As long as you encrypted it with FileVault, there is no need to erase it. Its contents are utterly useless without its password.