For me, anything 25 FPS or higher is 100% fine and I’ll be enjoying my time. I never play competitive online shooter games ever, though. All single player ones like GOW and the likes. I game on a 60 Hz 4k monitor. GPU is AMD RX 6600 alongside Ryzen 7 5700G and 32GB RAM. My games are set to meduim most of the time at 4k. Demanding titles are on low. Surprisingly, GOW and GOW Ragnarok are both set to ultra and I still get around 40ish FPS.
I feel like 20 FPS would be OK for me if I had absolutely no ability to get at least a 25. But 15? 16? That’s like very jittery. I remember that happening on Alan wake 2 and it was playable, but to be honest I was kind of annoyed with it.