In those days, we would usually read the manual when we needed to dig past a surface-level understanding of how things work. The manuals are dry and dense, but they're much easier to read with modern niceties like "Ctrl+F".
IMO, this is one of the reasons that people recommend using software with a long track record. If you have a question about some parameter in a systemd service script, and the internet doesn't have a ready made answer, the details are all written down in the manual.
https://www.man7.org/linux/man-pages/man5/systemd.service.5....
Plenty of modern tools have comprehensive detailed docs like this. Python, Go, even most widely-used JS frameworks. The primary sources are often downranked in search engines because they don't sell ads, but it's a good idea to find and bookmark them when you start working with a new technology. RTFM!