How should I wipe my computer that is running qubes? I want to be able to sell my computer. I don’t see an easy built in option that windows and macs seem to have.
So I’d download it in an appVM and run it from there to wipe the whole computer?
Search for “secure erase” on this 
page. Then follow from there.
You could probably find answers to this yourself. Really, for best results, melt it down, I guess. 
You don’t need to do anything, just run the Windows installer and format the drive.
Qubes OS uses LUKS encryption, even if someone tried to recover the original volume they can’t read it without your disk encryption password.
Some BIOS/UEFI come with the option to secure erase your HDD/SSD.
IIRC it is enough to wipe your luks header.
Archlinux has a great wiki, see 1.3
https://wiki.archlinux.org/title/Dm-crypt/Drive_preparation