My question is: is there a document (or collection of documents), that describes (in sufficient detail to work with it) the design decisions that are specific for Ubuntu and thus distinguish Ubuntu from other distros / distro families (like CentOS, Debian, Red Hat etc.) ?
That is, I'm not asking for a technical introduction to Linux in general intended for a Linux novice, but for a technical description of Ubuntu in specific aimed at the experienced user / admin.
Background: Having worked and lived (as a non-IT-person, but hobbyist programmer) with Linux systems for some 20 years and with Ubuntu since 12.04, I feel pretty confident with looking "under the hood" of the system and making adjustments that may not be possible from the GUI. Also, every now and then I'm inclined to try to find the reason for some unexpected behaviour or to resolve a problem myself for which I cannot find a solution on the web.
Doing this, I find it sometimes very difficult to figure out how things work in the first place. As an example (only), with my relatively fresh 18.04 install, I notice that the user switching fails every now and then. Googling, I have found out that this apparently coincides with a lightdm crash which is "persistent", i. e. restarting the lightdm service fails until I reboot. Now I'm stuck with understanding why this fails.
Here I'd like to have some kind of documentation that describes the system "under the hood", e.g. what software components are used (in which versions), how system startup works, how services are started, what is configured where, and so on. The "official Ubuntu documentation" for the desktop apparently is aimed at the desktop user only, not at somebody with my ambitions. Information Google gives me, in contrast, is very diverse, often contradictory, often outdated, and so not very reliable. This why I'm looking for a reliable single point of information about my system.
Thanks for any help!