I might be wrong here, but since Pix is part of XApps, it wouldn’t be available in the first party repos of any fistrobither than the Mint spins.
Perhaps you could add an external PPA:
sudo add-apt-repository ppa:embrosyn/xapps
sudo apt update
sudo apt install pix
The project hasn’t had a stable release, and yes, it does certainly need more testing to uncover edge cases.
Yes, MIT bad, but one must not diss on the project just because it has been written in Rust.