@DerEchte
Hi I watched your video.
I haven't seen many recent videos of you, the last one I remember, you were playing in a tournament against a teen girl [I think you lost]. Compared to that one, I think you've improved overall.
I think you should tell Sergey not to put a Tshirt of the same colour than the wall, and that he should throw the ball more when he serves ! also change the orientation of the camera to landscape !
Regarding the match itself, my impression is that the technical difference gap between the 2 of you is not that big, but yeh, he's a better player.
Sorry to say that, but what is the most striking is the difference in the level of fitness between both of you. So many times you make a miss because its not the first shot in the rally, you look either tired, or can't make the effort of adjusting a little bit your footwork. you miss more FH than BH and the cause is the footwork. One can make good BH just with good technique, - the first point of the video with 2 consecutive BH is excellent - but one cannot make good FH without using properly his legs and good footwork [unless the ball is coming straight at you]
I agree with all other comments saying that you are too tense and should relax, and look for more consistency before anything and eliminate unforced errors - like the one on the 2nd point of the video, ball is coming to your BH which should be your strong shot, but you rush it and put too much power, I think you should wait a bit more, getting down more on your legs while waiting and play it with more spin and placement rather than power.
I noticed a technical mistake that you did a few times, on your FH like at 0:50. Ball is coming to your FH. yeh you should move first your left leg as you do your backswing and while swinging transfer your weight forward ending on your left foot. But, even if you're late to the ball - wgu, you should absolutely try to recover your balance as you make the shot and finish on the left foot. Here you're making some kind of jump (and your upper body is going up as well) and we can see clearly that you put your left foot THEN your right foot when all is done.
I believe you should always be thinking about keeping this balance at all times when doing a FH, it may mean to execute a softer or replacement shot in FH, but if you don't do that, you will keep making mistakes and even if your shot is on the table it will be a weak shot AND your recovery will be late anyway so you can't get the next ball.
at 5:20 you do 2 FH in a row which are on the table even the ball is a bit far from you because this time you do end on the left foot.
Also, make the effort of keeping a good stance at all times. On FH (more than BH), you have a tendency to move straight up your upper body when you execute the swing. I think it is to compensate for the lack of power from the legs. Anyway its a bad habit.
Regarding short game / receives, you do make some mistakes but you do make some good shots, you sure know how to do them, its about percentage, and notably moving a bit more quickly to the ball.
Regarding matchplay, he didn't (need to ?) do much, he won with your errors mainly. For example i didn't see him make strong 3rd ball attacks which score the point immediately. You often blocked his opening loop without problem. But I think you didn't have tactics to put him out of his comfort zone. I think serving more to his short FH and test his flick and in/out footwork could be a tactic. or pinning him to his BH serving with inside sidespin (shovel / hammer/ BH) serving from the middle or FH side or the table, - and then opening with a slower spinny loop taking less risk and going for consistency.
I'm not saying you'll beat him next time playing like this, maybe he's got some margin, but if you pay attention to all these things, he'll need to show us much better TT to beat you.