https://store.steampowered.com/app/1701430/Mythos_Ever_After_A_Cthulhu_Dating_Sim_RX___Other_Soundtracks_from_2021
So, it's not only the soundtrack for Mythos RX, but for every single 2021 game as well! As long as it does not have a dedicated OST DLC of its own, it is in here!
There are even some from games that have yet to be released!