Project+ – the spiritual successor to Project M – has been updated to version 2.4. Included in this update are four new stages, new costumes, visual revamps for others, minor character polish, a couple of bug fixes, and character-specific adjustments for Bowser, Captain Falcon, Donkey Kong, and others.
See the patch notes on the official website. To get Project+ on Linux/Steam Deck, head over to GitHub and download the AppImage, the launcher, and the SD card. Extract the contents of the launcher and SD card, launch the AppImage, and point the emulator to the path of your default ISO and sd.raw files. Launch Project+ with the launcher .elf file.
If you want Project+ with more characters, I have a guide for PMEX Remix.