I've been reading some articles about mobile Linux and many of them state one must be an "advanced user" or that the software isn't secure. How true is this?
I already use Linux on my laptop, but I'm not a software developer or anything like that. Would I be able to slap a new OS onto an old Android phone and be on my way, or would I run into problems?
Linux phones lack in all aspects compared to AOSP: security and privacy enforcement (mandatory sandboxing, permission control, full-system MAC, verified boot), usability and compatibility with the mobile app ecosystem. The much better approach would be to get a Google Pixel and install GrapheneOS. This will get you a very secure and private smartphone with almost perfect Android app compatibility. Recommend reading about Linux phones on madaidans-insecurities.github.io