@majorandme i have the rift s too and i got it to work through steam. i have the open beta version. go into steam, open the steam vr, go into its settings, pic2;point2 it will say something about openxr,choose it, then it will change into what it looks in my pic2. then downleft on steamlibrary Add game (point4) and choose the mt version. after that choose it from your game list and should look like pic4, on the right side i had to choose "needs vr" (point5). after that it worked. im not shure if you need to apply layers and that meta plugin (points 2 and 3). hope this helps you and others with Rift S.
oh and i have that in the properties of the game in steam too. dont know if its needed after u choose the "needs vr" option but have it anyway