Mate I was in the same boat, especially in Gr3 and when we had brands hatch, road Atlanta and spa then suzuka it was a bloodbath for me. Some unsolicited advice

For me, I just decided that I would take it on the chin and dedicated myself to only racing Gr3 until I got the hang of it - took me all of those races i just mentioned and it was a miserable massacre for 4 weeks and dropped from 33k to 12k DR and honestly thought I was on for D, but then something finally clicked and had great weeks at Reb Bull and Kyoto. I think the race craft is purely just time behind the wheel - I'm much better with when to let people go, where to overt take/where to bump draft (still an absolute beginner but better than I was, lots to learn still). You've definitely got the raw pace for A mate.
Think we are in the same boat with new tracks as I started only a little before you, if deffo helps when it's a repeat track to be upto speed quicker.
Yeah Shadow of the Ertree was rough, I completed it but had to summon someone in for the finally Radhan fight as it was just obscene. If and when you are looking for a new game, I can't recommend bloodborne highly enough, same studio as Elden Ring and I enjoyed it more than Elden Ring.
Ok - I'll take the recommendation and will give it a whirl, playing Black Myth Wukong at the moment when i get too frustrated with GT7