Realtime (ctrl-R) not working

Toggling Realtime in the editor viewport has no effect anymore. It was working fine yesterday and stopped working today for no reason I can think of.
It’s a big deal for me: with Realtime Off, I get 120 FPS and Lumen still kicks in: the FPS gets down until the lighting gets recomputed and gets back to 120 which is great.
If only I knew what I did wrong, any clue folks?