I had a car where the shifter broke to the automatic transmission - it was simple enough to bypass the neutral safety switch and then I could just leave it in Drive all the time. Just had to make sure if parking to park on an incline if I wanted to be able to roll back out of the parking space.
Eventually I cut a hole in the floor and welded a shifter direct to the transmission.
Related to this, one of my stories about turning a car off.... I was a misguided youth rebuilding a Subaru that sat in a field for a long time. It had many problems, but overhauling the engine solved all of them (or so I had naively planned). I remember the first drive I took with it after getting plates on it. Right after filling the tank for the first time, I went to Taco Bell, bought a victory taco, and went to a parking lot to look over my city and eat. When I tried to shift into park, the cable snapped. Dejectedly, I sat and ate the taco with my foot on the brake, warming the ATF while I figured out what to do. Several factors stacked against me, including that I lived on a hill, didn't have a garage, the e-brake was rusted, and it was January in one of the snowiest areas in Michigan (3-4ft snow banks in most places). I knew the next time I flipped the car off would really count, because I would have to hot wire the NSS or fix the cable to get rolling again. Parking in the winter is a huge problem too: you will get towed or fined for getting in the way of snow removal. I ended up precariously "parking" the car in drive near my house with a combination of gravity and a snow bank. I set the ramps up, crossing my fingers that they were spaced correctly and that I would succeed in getting on them on the first try. It all worked out, and when I finally turned the car off, I felt pretty intellectually victorious.
On the plus side, I learned so much about how cars work that I can fix a lot of things now. My personal peak was going from “uh-oh, the alternator on the Oldsmobile died” to having replaced it with a new one from the store in 43 minutes.
Troubleshooting is a lot harder for a variety of reasons. Things are hidden away under plastic panels, the vehicles have a lot more electronics, and everything is fit into much tighter spaces.
Still, between YouTube and enthusiast forums dedicated to whatever model car it is, you can usually do a lot. Typically if something goes wrong on your car, the same thing has gone wrong to a lot of other folks with the same car and someone has posted about it.
If you're handy enough and have the right tools, an official manufacturer shop repair manual is what you really want. (Chilton is better than nothing, but you really want the manufacturer repair manual.)
But... some things are just a pain in the ass w/o a lift and the right tools. Find a good independent mechanic for older cars (easier said than done) or just take it to the local dealer for cars still under warranty.
Half the troubleshooting is being able to recognize and describe the problem in such a way that you can search for the solution. Knowing what "sluggish acceleration" is vs "RPM limited at 3k" vs "cold-start no power" is half the battle.
YouTube is substantially better than the old Chilton manuals and arguably some better than the manufacturer repair manuals (many of which assume you have an entire dealer shop's worth of tools). A number of videos (and even some of the Chilton manuals) will have variations on the process that either avoid the specialized tool (at perhaps a bit longer of a process) or a workaround that greatly simplifies the process.
My dad had a good collection of tools, and I bought a Chilton's manual from the shop. Between the two of them, I basically had a years-long shop class with illustrated instructions on doing basically any repair to a car. It was a great way to learn some engineering skills, too: once you learned how a part was meant to work, you could better reason about how to repair or replace it. Jalopy though it was, I loved learning how to fix it.
That said, although the barrier to learning is much higher now, I appreciate that our Toyota never needs any repairs of any kind. It just boringly starts and drives, every day, in all conditions.
Eventually I cut a hole in the floor and welded a shifter direct to the transmission.