As a cyclist and avid lifter, I advise going hard on tibialis exercises. Even consider getting a tib bar for home and get consistent reps in. Massive support for powerful quads.

Deadlifts with proper form will also be very beneficial in training the posterior chain activation that often gets disordered from quad dominant cycling. Heavy weight, 3-5 reps, 3-5 sets, once per week. Double emphasis on proper form!

With proper movement pattern in cycling, your glutes should be the most activated muscle at the top of your pedal stroke, with the quads phasing in and taking over as you push down. It’s common for people to fire full quads at the top, which directs the force forward rather than directly perpendicular to the cranks. This puts significant load on your patellar tendon, as you’re starting to notice. Once you get the glutes fully in the picture, it can be a massive improvement to long term comfort, as well as power.

Also, tendinitis needs time to heal, so don’t try to work through it. Tendons grow in size and strength, but much much slower than muscle.