Go back to disk utility and show us how it looks.
Restarted the computer, only this time time it only gave me the option of installing Mojave. So I’ve done that, and am now manually updating to big sur. It does appear that everything has been wiped properly now at least.
@Nef started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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Go back to disk utility and show us how it looks.