RE: Leather case aging and "conditioning" to allow faster patina.
I had really never gotten into the brown case; since my 5S (was it 5S? Time passes. Maybe it was my 6+ that had my first Apple leather case.) I had always gotten an Apple leather case, but in black.
Few weeks back, I looked at this thread and started thinking....
Picked up a saddle brown for my XS Max and it really felt slippery and just wasn't as dark as my liking. So, a little experimentation. First, I cleaned the case completely with fingernail polish remover. I felt the acetone in the remover would take off the clear finish Apple applies to the cases new, and after a few cleanings, the case felt much tackier and easier to grip.
Next, I used Lexol leather cleaner. If you are not aware of Lexol, it's top notch. I've used it on car seats for decades now, and super easy to use.
After this, I used Lexol leather conditioner. Unlike other conditioners, this will dry and not leave a sticky residue.
Once it dried completely, I stuck it back on the phone and started using it. After almost a week, the change is very noticeable on the case. It is darkening nicely on the edges and corners.