Cfrgtkky

Disclaimer:
Please forgive me if I don't provide enough info/forget anything, I'm new to this.

I'm using Ubuntu 18.04

Since about a year and a half, I've been using Ubuntu on a ThinkPad P51. At some point, a friend of mine recommended i3wm. I started using it and ended up loving it. I first did not know half of what I was doing, but I did realize that if I didn't touch too many scary things, I'd be fine.

Fast-forward, half a year after using i3, I had started customizing it a lot, and tried using it with a second monitor, to no avail. I did do some searching online, but nothing seemed to match my problem. I also remember having had a booting problem sometime somewhere along the way, could have been a distro upgrade issue.
This booting problem was related to login problems, like the one found here. I posted earlier about this here.

At some point, I tried to switch display manager (for a fancy login screen, something with lightdm-webkit2-greeter) where I, due to ignorance, ended up entering
sudo apt purge dbus
and did a reboot (because of an unrelated bug/warning about dbus accessibility, that showed up in the console when trying to solve the lightdm issue). Turned out that dbus was kinda important for intercommunication of processes, I was unable to fix it without a very painful reinstall and backup process. I learned not to purge dbus and got my system back after a lot of work.

After a while, I tried the second monitor setup again, didn't work. Neither i3wm nor Ubuntu allowed me to use external screens. After looking at this post about Ubuntu on a Lenovo ThinkPad P51 article and following the instructions, I did get some kind of working system. However, my brightness control was nowhere to be found (ThinkPad P51 has specific multimedia keys for both brightness and volume, which need to be set up via keybindings in the i3-config, but that's not too difficult, and was not the issue). I literally could not adjust brightness anywhere. I looked at kernel/grub parameters which I did not really understand, such as acpi_backlight=vendor (those need to be set in /etc/default/grub)

Just now, wonderfully, through a lot of combinations of programs, settings and purging and reinstalling drivers, It finally worked. I have no idea what was the exact trigger and have no clue how to reproduce this.

All of this seems very much related to the fact that the P51 has two graphics cards, one Nvidia and one Intel. There's one specific setting that bothers me most: I cannot use the Hybrid Graphics option in BIOS when having selected the Nvidia drivers with nvidia-prime, only Discrete Graphics work. (options for the drivers were prime-select nvidia) and prime-select intel The problem here is that Discrete Graphics are much more power consuming and drastically decrease battery life. Before all the trouble, I had been using the Intel drivers, with the Hybrid Graphics option selected.

My question: Are there any people with the same experience, and could anyone explain to me why this is such a pain to setup? I would also like to know if anyone could tell me what I need to figure out and remember/write down to be able to reproduce this when I shoot my system to shits again.