I am also an old fart that moved from nikon to the sony a7r1v about 9months ago.
The transition was not easy, and I found the sony menu system to be awful. I just about threw the camera into the lake several times.
Mark Galers videos, and book, were very helpful.
What I ended up doing, which actually worked, was to just go shoot. This is still just a camera. I put everything in manual, and just went and shot.
Each time out I added a couple of settings that would make things easier, and slowly things fell into place. Now everything makes sense, although I am still molding the system a little. With everything being programmable, you can get this thing to do anything you want, you just have to know what you want it to do.
Gary