You're totally correct, you can do pretty much anything you want in Android running in the background. But the post you replied to is referring to Stopping an app .. via the app info in settings. In this case it stops the background service component until you launch it manually again. Noone apart from power users and developers would do this though.. most people likely don't know what the stop app function does.

There are OS battery optimisations which kick in eventually though, which result in most non system apps to be stopped automatically to save battery. Once again, they won't startup in the background again until being manually launched. This is my general understanding gained from working for a couple of years on an Android app that runs in the background and receives silent notifications.

I don't develop apps for Android, but I do for iOS. I will assume that my operating systems knowledge though is from Windows/Unix. To use Windows terminology, an app is running either as 'manually launcher's or as a service (system launched). Android (at least my Honor phone and any tablet I ever used) gives me the ability to manually intervene and change the auto-launch and the background running. I windows that would be things found (and 'killed') in SysInternals AutoRuns.

I don't leave 'everything on default' in the power/background running settings, and thus I don't give the apps the option to do what the device decidsd. Plus with the firewall I Block all the nasties (e.g. 31.13.x.x - FB, or the various IPs for ads and tracking).