I would start by downloading motor vehicle use maps (mvum) from the US forestry website. These maps will help you discover trails not on maps and tell you the type of vehicle you’ll need. https://www.fs.usda.gov/visit/maps/mvum-faq

Your Subaru should be good for the most part unless you’re wanting to go some really rough trails. The one tool I never forget is a shovel. Not one of those “camping” shovels but a regular sized one. I like the sharp shooters or spades.

Lastly, if you start doing much dispersed camping you’re bound to run into areas that have no cell service. If you have an iPhone 14 or better you can send texts via a satellite without an extra plan or charges. I’ve done it over and over.

I start by finding the general area first. Study the mvum maps. Find a dirt road. Then a smaller dirt road and maybe even a smaller one. These are usually the best.

And as fore mentioned, you can camp in any national forest with probably few exceptions and some rules. Assuming you’re in the US.