As someone who way long before the LLM age had small patches accepted in several dozens of projects I've been using, I can assure you that this is just a matter of mentality. All I needed to be able to do that was to stop thinking that "nobody has done it so far, so it must be hard" and just do it. Sometimes I failed, but more often than not it turned out it wasn't hard at all and nobody has done it so far simply because nobody cared enough to attempt it.
> Getting software to compile in order to start hacking on it used to be enough friction that I often wouldn't bother.
Not my experience at all. Usually the only limiting factor is the size of the project. Compiling a web browser on my 7 yo 13" laptop is a miserable experience, but compiling most of the desktop components or utilities is and has always been a breeze and, in my experience with both Debian and Arch, just a matter of grabbing the distro's source package. I even do it on my phone these days.