The Yamagi Quake 2 patch is a lovely way to play the original why it even includes the OST

(apparently this source port may not have the OST included anymore but you can extract the OST from the remaster and do with it as you please)

https://www.yamagi.org/quake2/

Side note do yourself a favor and enter "ogg_ignoretrack0 1" into the console menu (press `) if you don't do this then the music will turn off anytime all objectives are completed and trust me you don't want that to happen but this is only the case for Quake II vanilla Quake II RTX wont have this issue

With Quake II browse the local files, go to the base folder there should be a music folder in there. Now simply copy the music folder and paste it into the Quake II RTX base folder and there you go now you can rock out to one of the greatest soundtracks ever and gib Stroggs with ray tracing technology
Edit: If the music doesn't come on try typing "ogg_enable" into the console
Side note you could make a new folder in Quake 2 RTX and call it music then copy and paste the OGG files from Vanilla Quake 2 music folder into it and as long as you have the OGG files you could add your own custom soundtrack from anywhere