First, download FMOD Engine version 1.10.20 from https://www.fmod.com/download. You need to create an account to download. Then navigate to the downloads page, click FMOD Studio Suite and under FMOD Engine click Older and select 1.10.20 in the dropdown. Then click Download on the line with Linux. Place the downloaded file at the root of this repository.
Install SDL2's devel package with sudo apt install libsdl2-dev. This installs the required dependencies for building SDL2.
Now, run ./build.sh and wait for it to complete.
This will create a file called celeste-libarmhf.tar.gz. Extract this in the Celeste game directory.
To play the game you need to install the Mono Runtime with sudo apt install mono-runtime
You can now launch the game by running ./Celeste.sh from the game directory. Enjoy!