Hi there,
I have the same issue as the OP. H265 videos won't play (stalls at just a frame or 2). I've tried uninstalling klite, hevc extensions, reinstalling them, and applying the codec tweak tool fixes per your suggestion, but still to no avail. Any other ideas? I'm using SteamVR as well with WMR (HP Reverb G2) with an Nvidia RTX 2070S.
Any help would be greatly appreciated!