I guess I found the problem, at least in my setup. I went into the UserCfg.opt file and changed DLSSG 0 to DLSSG 1 (mandatory) and frame generations still greyed out but if I use an external fps counter like FPS Monitor or the one from Nvidia Geforce Experience (alt+R to display it) it shows more than 100 frames in 4k
Apparently it’s a UI bug but it seems to be working.