Posting this in case some wayward soul googling "forgot sudo password bazzite" may come across it.
Installed Bazzite on my ROG Xbox Ally a while ago and couldn't remember my sudo password. Couldn't even remember setting one. Tried all my usuals, none of them worked. Looked up tutorials on how to reset it, couldn't figure out the grub menu bash thing. Was about to give up hope and just perform a fresh install.
Then I remembered that one of the first things Bazzite asked me to do was sign into steam (I used the version of it that was configured to work like SteamOS) so I tried my steam password and it worked.
Maybe it tells you that and I just forgot or wasn't paying enough attention, but my steam password is not something I normally use, so there's a possibility that it gets unintentionally set as a sudo.