A first user in Debian is not automatically a member of the sudo group so can not do anything which needs root permissions. However that user can be...
Go to the boot repair page at the link below from one of your functioning installs and use the 2nd option explained on that page as it is more up to...
I have a working Mint 21.3 install on the drive so I will stick with that until 24.04 comes out. Right now 24.04 installed but gave me a lot of grief...