I had severe knee pain (ruptured VMO) in 2017-18 and again 2018-2019. Could not ride at all. The root problem was of postural origin. Cortisone did not help. Eventually strength work prescribed by the last of three different physios helped resolve the issue, but learning to feel and understand how I moved wrong in everyday situations has been just as important. Still need to be mindful.
I too did tons of glute work, which helped, but did not resolve the issue. Eccentric quad excercises (with ‘tirante musculador’ belt, or similar) were the same.
If you dont mind me asking, how is your control of the core and the si joint and have they been addressed by physios? On the bike and off? Probably they have, but i ask anyway because in my experience all the hip work had a limited impact before these parallel problems were also addressed. Key excercises for me involved core control plus hip extension on one side and flexion on the other. I still do them, as they are good beyond the immediate therapeutic use.
These days I ride pain free so there is hope, and it has been like this for more than a year, but damn it was frustrating.
Of course I also changed bike position but I think this was more to utilize better hip mobility and power on the bike after solving the main issues. My pedaling changed quite a bit, more glute these days.
Hope you get the knee sorted!