I’m not an expert, so take this with a grain of salt.
I think most importantly, remember that your body is unique and you will develop your own squat. Other people like Rippetoe have recommendations on how to do it, but no two people will ever look the same.
If you’re plateauing at 90kg/200lb, then you need to get stronger. Obviously. If you can’t continue progressing, then either regress and start with Starting Strength (the program, not necessarily the exact movement) or go where you’re from and follow 5/3/1 for a while. Those are pretty good.
Right now it looks like you’re dropping quite fast, and putting most of the weight on your quads.
So really, what are your goals?
If you’re training for mass then slow down a bit (don’t glo slowly, just control it), and maybe consider front squats for your quads. And eat. And gain weight. That should do it.
If you’re training for strength, then you should consider sitting back a bit more. Not a ton - if you’re squatting raw then you don’t sit back as much as a geared lifter, but more so than you are right now.
In that case, I’d do glute-ham raises (GHR’s), hip thrusts, back extensions, and goodmornings/RDL’s. You should be doing GHR’s anyway - a taller skinny guy needs to protect his knees and these will strengthen your hamstrings, which will help keep them healthy. Do 3 sets to failure before every workout as part of your warmup. This will add up and seem like a lot at first but that’s fine because your hamstrings can never be strong enough. Read this if you want more information: The Glute-Ham Raise from A to Z
For the other accessory movements, like hip thrusts (How to Hip Thrust - Bret Contreras), back extensions ( 150 Pound Back Extensions for Glutes & Hams ), and goodmornings or RDL’s (do RDL’s if you’re inexperienced. They’re “safer.”), you can do them throughout the week. None besides the GM/RDL are very stressful.
You want your lower back strong so you don’t round it, and your upper back strong so you don’t collapse. Rowing should be good for the upper back.
Basically, it depends on your goals. Your squat doesn’t look horrible. But you should slow it down, and squat the way you should to achieve your goals.
Again, for mass, slow it down a bit, and consider front squats, since no one really squats expecting to put on much hamstring mass. And eat. And eat more. Just gain weight. You’re young enough and small enough that you won’t get too fat if you’re smart.
And for strength (powerlifting), sit back a bit. Shift some of the weight onto the posterior chain, and you can strengthen those muscles with GHR’s, back extensions, hip thrusts, and other weighted hip hinges such as goodmornings or Romanian deadlifts.
Either way, consider squatting more frequently. If you’re not recovering well then do an easy squat, like goblet squats. Frequency usually makes a skill come faster.
And either way, your lower back should be taken care of with those movements ^^ but your upper back will strengthen your squat no matter what kind you do or what your goals are, so do lots and lots of rows, and some vertical pulling like chinups. (Chinups will give you a better idea of how weak/fat you are, but rowing is more important for shoulder health.)
Using a belt if you feel it’s necessary is fine, but try to not become dependent on it. Oh, and when you breath, make sure you breath into your stomach, not your chest. Your shoulders shouldn’t rise when you breath. It’s all into the stomach. You want to push out and brace it. Don’t think about sucking in and flexing to show off your abs. Do the opposite and pretend you’re pregnant by shoving out and flexing it to protect your baby.
That’s a lot. And I didn’t condense it very well. But you get the idea. Your squat will always be unique so follow your goals, practice it often, and consider taking a few steps back to make sure you’re doing it right.