If you're like me and you can't feather the accelerator, you only drive in automatic, or can't concentrate because of all of the traffic, these are the things that helped me the most, and I didn't see them mentioned anywhere.
I used the Formula Drift #118 Nissan 240SX with a tune by Don Joewon Song for the S2 923. It is the only AWD Formula drift car and when you mash on the gas the rearend doesn't slip like all of the other ones. With traction control off I got all 20 drift zones in it. The harder ones (especially S-Bend) I did my best scores in the rain. I always stay in automatic.
I did all Fortune Island and Lego Valley drift zones in the Hoonigan Gymkhana 8 Ford Fiesta with the Kelte1986 A800 tune.
You can rewind many many times in in Horizon Solo. I've rewinded up to 20 times in one zone without losing my score. The only time I can't is when I'm online.
For all PR Stunts:
The traffic. The ghosting totally bugs my eyes and I can't focus at all. I found myself instinctively trying to avoid cars as well. Also, they tend to get in the way for Danger Signs and Speed Traps.
Make sure you are in Horizon Solo and are in the vehicle you want to use. Complete any story chapter, even if you've already done it, as long as you get one star and complete it (not quit) it will remove all traffic. Do not fast travel or change cars or it will come back, so I picked whichever one was closest to the stunts I wanted to complete. You can change your settings for Traction Control, etc. This trick also works on Fortune Island and Lego Valley.