Sounds like it could be meniscus related, this can cause issues into end range extension. Try a seated knee distraction. To do this: sit over the edge of a high table or bed, something your legs can dangle while seated and relaxed. Strap a pair of heavy-ish ankle weights (5-10#) on your ankle and let it dangle for 5 minutes. Do this, then do some quad sets, repeat a couple times per day.
I am a PT and use this with patients who come in with this issue and have had pretty good results. I’ve also used this myself as I have had this problem in the past. Very heavy band (EliteFTS has some good ones) TKEs to strengthen the quad at extension; single leg RDLs, nordic HS curls, and glute ham raise for eccentric hamstring strength are key exercises once the pain at extension has mostly resolved.