Stuck in Plat I

Hello I was interested if anyone can give me some advice on how to become better. I am mainly interested in opinions of Diamond players because I've been winning games from Plat V to Plat I with a winrate of 70-80% and now I am sitting maybe at below 50%.

I am literally stuck in plat 1 and it really really sucks :( Are there any tips that might help me?

I usually play as a jungler/mid and even when I do get jungle I still lose (7/0/6 xin to 7/7/7 , 15/6 kha to 15/10). I have no idea how to win games and right now I am desperate to get to atleast diamond V. There are many diamond players against my teammates who stomp them and I can't be on every lane to help so I usually have to choose which lane has to get severely stomped(usually its either top or mid).

Toxicity is way too high and I can understand that because everyone tries to get plat or not fall out of diamond V but it makes others lose focus off the game.

I also gave up on duo/trio/full premade because it seems like whenever we are more the worse players we get on our team(we were 4 premade and had a adc kog maw with smite on bot and he said that he knows what he's doing but ended up in 2/9 I believe).

Yes this is a cry of help post anyone is welcome