Just start thinking about speedrunning, watched alot of GTA V speedrun and wanna try Trevor% since its the shortest (excluding all stunt jump) But have been learning for couples of day now but only know the strat for like 2 or three missions, and still cannot finish 3 of them in one go without dying or losing lotta time,

So I think about some easier game. And I don't have any console except just ma pc and my phone. What should I speedrun? (Ofc I've been thinking about google snake lately)

If you are enjoying learning GTA V, persevere. Expecting to learn any strat well in less than a week seems like high expectations to me. It takes people months, sometimes years, to really get good at a game.

Start off small and think of it this way - you already know strats for a few of the missions! Fantastic already. Do the rest of the run casually, then try to learn more strats.

If you're not enjoying it - pick literally any game you do enjoy. If it's google snake, cool. Nobody can tell you what is good "for a new speedrunner". It is all down to what you enjoy and what you are willing or able to learn.