Do you support mysql instead of sqlite for the db backend file in Urbackup server?

Do you support mysql instead of sqlite for the db backend file in Urbackup server?

I would venture to suggest “no”. BUt, that doesn’t mean you couldn’t use mysql yourself. After all - it is open source and I can’t imagine there would be many changes.
Personally, I can’t imagine a reason for preferring to go “off standard” for a self-contained backup system. SQLITE is very comprehensive and ideally suited to urbackup. Perhaps an explanation as to why you would wish to use mysql might produce some helpful hints/answers that may better serve your issues.

For the security reasons we are trying to use mysql. We wanted to protect the backend .db file with username and password.

If you are using a container - it should be relatively easy.