Dolphin, the GameCube and Wii emulator - Forums

I did, multiple times.

Something is misconfigured on your system, then. Could be that the PPA repo was not added.

I also tried https://wiki.dolphin-emu.org/index.php?title=Building_Dolphin_on_Linux and it said I needed an updated version of cmake, but I ran
sudo apt-get install cmake pkg-config git libao-dev libasound2-dev libavcodec-dev libavformat-dev libbluetooth-dev libenet-dev libgtk2.0-dev liblzo2-dev libminiupnpc-dev libopenal-dev libpulse-dev libreadline-dev libsfml-dev libsoil-dev libsoundtouch-dev libswscale-dev libusb-1.0-0-dev libwxbase3.0-dev libwxgtk3.0-dev libxext-dev libxrandr-dev portaudio19-dev zlib1g-dev libudev-dev libevdev-dev "libpolarssl-dev|libmbedtls-dev" libcurl4-openssl-dev libegl1-mesa-dev libpng-dev

so I assumed cmake would have updated.