As per attached screenshot, saying Collection site administrator added. That account is adding itself and the "All Users" group to sites admin. I've tried to manually remove both "All Users" and azuread account from admin but it just adds itself and the group back a few days later.
My sharepoint is not in use yet, and I'd like if all my users could not edit my pages. Can't figure out where that automatic option would be, I've searched all classic and new sharepoint admin center options, maybe I missed something.