cyclezen

so my few cents. Won't go into the med argument. But you likely have no chance that they'll (medical help) help you solve the cycling issue.
If you believe the 'condition' is now persistent and an injury, then maybe consider treatment.
if you don't think it's persistent, then you need to adjust your cycling to remedy the issue - if you want to use 'clipless'.
If you want an 'intermediate' step between open platform and clipless - consider adding oldschool toeclips, without the straps, for a while.
There are slight wider toeclips which are toe hold only - no straps, worth cosnidering.
Otherwise, if you want to progress to clipless - clipless requires much more exacting positioning of everything, to work properly for a rider.
Once a rider gets into multi-hour rides, the setup becomes more critical.
I won't go into my setup methods right now... and there's an adjustment to riding technique - gearing choice to be made when dealing with more overall weight.
I'd start with toe clips and see how that works.
Just a quick tip...
With most platform pedals, if you ride with your feet in a consistent position on them... Look at the soles of your shoes. They should/might show the pedal cage marks...
That will give you the current foot position on your current pedals/shoes. Hold your shoes to the pedals, to match those marks, with the pedals on the bike and the shoe/pedal/crank roughly horizontal to the ground.
Look at the combination relative to fore/aft AND importantly the ROTATION of the shoe (and your foot) on each side. THAT is the orientation you want to achieve in your clipless setup... (for now). There are further considerations, for the future, on power delivery and muscle/pedaling usage...
this:

Thx
Yuri

jay4usc

have you tried foam rolling your thighs? If not look it up on YouTube

cyclopath256

Thank you all for your answers! There is some really valuable content that you have put together!

First and foremost I am going to make an appointment with an orthopedic specialist.

After that I will consider the fit of my bike. There I've got a little issue. I bought my gravel bike in April when all the gravel bikes at bike shops were sold out because of the pandemic. It was probably quite dumb of me, but I bought a bike online. The frame was probably a bit too big and I solved it by getting a 3cm shorter stem. Now the size feels just right, but practically no professional has seen me ride it. I did go to a bike shop and asked them to check if it fits, but they didn't really check it properly. I mean, I get it, why should they bother if they weren't the ones who had sold it to me? (I did offer them money for this service, but they refused)

What would you do in my situation?

cyclezen

So, yes, have the knees checked out if you're worried or it feels 'persistant'.
Bike & Fit.
When I check out my bikes which I rode/raced back in the late 60's, 70's and even early 80's (some which I still have...) - they were all too big! (compared to what I ride now... LOL!)
Nothing extreme or unusual - was just the way we all sized back then.
Having 'short' seatposts, as what was available, made 'fitting' very difficult and caused many to go too big. I laugh at this statement now, considering how many I admonished back then for getting too big a bike/frame. Back then, if you could 'stand over' a bike, without hurting yourself, you were in the sizing ballpark... If you were racing, you would certainly size smaller - which was still too big! LOL!
Bike 'Fit' is all about attaining a position which optimizies both your personal performance as well as minimizing the risk of injury.
Everyone is different (within a range of human values). And HOW and WHY you ride is a large determinant of position.
An MTB cross country rider will position differently from a DH rider. A road racing rider will position differnt depending if they're ride a TT bike/race, road race, criterium, or riding the 'track'.
Same goes for any number of variants, touring, commuting, shopping, etc. There are signiificant differences in position for any of these.
Then comes physiological differences which will affect all of these. ..
so... there is no one 'way' to do this.
I would:
1. find out how different your current machine is from what might be a good middle ground sized machine for your body. You could go to a reputable bike shop which has a reputation for fitting customers properly to bikes. Not one which 'fits' customers to current inventory. You could search out for an independent person who is acknowledged as a professional fitter.
There should be some basic measurements taken of your body. If that doesn't happen, then don't rely on their estimates/suggestions. Pro Fitters will get more in-depth on body/structure and questions regarding issues/prior injuries/other considerations & anomalies in your physical makeup.
2. Ultimately you should try to get a good starting point setup for 'position' for yourself. Position being determined by the 5 contact points you make on a standard bike - right & left pedals/feet, sitzbones on the saddle, right & Left hands on bars. Not surprisingly, there are many humans/riders who have variations in leg length/rotation/joint structure/leg angle in their left to right legs. Similar issues with the hands/wrists/arms&elbows/shoulders... Important to look at and consider all this in setup of a position. And all this can change, over time.
3. 'Position determines the bike frame and parts. If the determined position is not achievable with your current bike, then you'll have to consider your options, depending the direction you wish to take your cycling activity.
It is a journey, often and adventure... LOL!
Good luck and let us know how things progress.
Tschüss
Yuri