I don't know what I'm doing wrong

I don't know exactly how many games I've played on SR, but if I had to take a guess it's somewhere in the 4000-5000 range. My skill peak was season 4 at gold 3, and now that I got reset to silver 3, I can't carry out anymore. I don't really know why I'm garbage but maybe it's autism? I don't know... but it's really making me sad because I've invested so much into this game, money and time, and I don't have many friends at all outside league so I try to get social interaction through league (and I know that's a bad idea since most of the community is toxic, I try my best to ignore them), so it would really make me happy if I saw some results from something someone told me. I'm unable to see my mistakes, since most of the time mistakes SEEM like glitches, or straight up are glitches in the game. Take for example a legendary lissandra match that I lost. I ulted zed, and he w'd out of it. My ult hit zed's shadow. I had encased a shadow in ice. I don't even. I won't name anything else because then I would name so many things it would no longer be a plea for help, but a litany of complaints against this game. Can someone help me, please?