Well, Rum, my favourite YouTuber is Alessia, of Lazy Dancer Tips. Masses of free content, from 5 minute shorts to hour+ ballet classes. If it's your knees you want to focus on, she has a 16 minute video on that very thing - just go to Lazy Dancer Tips and then search 'knees'. But there's a lot on her channel that focuses on balance, strengthening calves, ankles, feet and glutes, all of which will help prepare you for trekking. I got into her workouts during the first lockdown, and nearly 4 years on, my plantar fascitis is gone, my tendonitis in my achilles sorted, and the pain from my right sacro-iliac joint and weakness and pain down my right leg mostly fixed. I still have to take care of it, but I'm no longer limping home from the 10 minute walk to the supermarket! Plié on! Wall sits are also good for knee recovery.
I will ask my brother who recovered from knee surgery to running 10k on roads again what exercises he did. Basically, physio/barre/pilates to strengthen muscles and improve alignment will work, but you usually have to do three times as much as the physio will admit, for four times as long.