Great work on your write-up. It was such a pleasant read! You were able to cover all the points. Here are some things to take note of though:
“As you read this letter today, I hope it could cheer you up, remind you of the past and motivate you for the future.” – It’s better to have an Oxford comma before the last part. “As you read this letter today, I hope it could cheer you up, remind you of the past, and motivate you for the future.”
“I have started my socialization” – This sounds a bit unnatural. Perhaps you can say “I’ve started joining” or “I’ve started taking part in”.
“As y know I have already worked as a volunteer on the Ural Music Nioght festival” – “As you know, I’ve already worked as a volunteer at the Ural Music Night festival”.
“Also I have” – “Also, I’ve”.
“I wish I would continued drawing them with oil paints, otherwise I will have to lose an important skill for my self- expression again” – “I wish I would have continued drawing them with oil paints, otherwise, I will have to lose an important skill for my self-expression again.”
“if you not shore” – “if you’re not sure”
“I’m firmly believe” – “I firmly believe”
“Looking foward to see you, Future Me. But in fact I don’t.” – These two sentences are very contradictory without much transition. Maybe you could write, “Looking forward to seeing you, Future Me…well, not really. I think it’s best we leave each other in our own times”. Or something like that. Be careful with the spelling of “forward” as well.
Try to use contractions more since this isn’t a formal letter. And be careful of punctuation errors.
Overall though, it was a pretty solid read. Keep it up!