Deleting your account is permanent. The option is deliberately at the very bottom of Settings, and nothing happens until you confirm.
Open Settings
Tap your photo at the top left, then Settings.
Scroll to the bottom
The delete account option is the last thing on the page, below everything else.
Read the confirmation
Tapping it opens a confirmation asking whether you are sure.
Cancel if you change your mind
Cancelling leaves your account exactly as it was. Nothing is deleted until you confirm.
Confirm to delete
Confirming deletes the account and signs you out.