Big Sur recovery partition booting as El Capitan

I have a Big Sur installation which I did as an upgrade. I decided I want to wipe the drive and install Big Sur from scratch. But when I booted to the recovery partition, I was surprised to see that it is the recovery partition from El Capitan.

I'm afraid to wipe the drive, because I don't want to be stuck with having to install El Capitan as my only option. I just want to erase it entirely and install Big Sur from scratch.

Does anyone have any recommendations for how I can do a complete clean wipe and start installing Big Sur from scratch on this machine?

Thank you in advance!