I am on Linux Mint 21.1 Cinnamon.
When I try to add the Dolphin emulator repository for Ubuntu (which should work since all Ubuntu derivatives are said to work) using the command "sudo apt-add-repository ppa:dolphin-emu/ppa", which is the command given in the installation guide for Ubuntu. When I execute it, I am given the error "Cannot add PPA: ''No supported PPA of this name was found.''.". Yes, I have added the universe repository. I have no clue why this doesn't work.
When I try to add the Dolphin emulator repository for Ubuntu (which should work since all Ubuntu derivatives are said to work) using the command "sudo apt-add-repository ppa:dolphin-emu/ppa", which is the command given in the installation guide for Ubuntu. When I execute it, I am given the error "Cannot add PPA: ''No supported PPA of this name was found.''.". Yes, I have added the universe repository. I have no clue why this doesn't work.