On 18.04 it takes like a full second, sometimes two, to open the calculator anyway.

They changed those apps to normal packages in 19.04 or 19.10.

Oh, I get it now.

multiple monitor support in Linux is high on my list of reasons I keep switching back to my Windows partition.

I suggest trying Kubuntu. I've been running 3 4K monitors for years, all works fine, including HiDPI support.

If my primary monitor is to the right of my secondary monitor, do applications open on the primary monitor or the 'left' monitor? Also, do applications remember which monitor they were last opened on?

Not the parent, but I've also been using KDE in a multi-monitor setup for years (I have a 1440p primary monitor, and two vertical 1080p monitors to the sides). In my experience, applications open on the primary monitor, or on the monitor that is "active" (i.e. if you run Alt+F2 to bring up a run prompt on your secondary monitor and launch an application from there, the application opens on the secondary monitor where you launched it.).

Yes, applications remember which monitor and even location on the monitor they were last at.

It worked very, very well on Unity. It also works with other DE like Plasma but I personally find it horrendous on other aspects.

I'll probably give Budgie a go.

If my primary monitor is to the right of my secondary monitor, do applications open on the primary monitor or the 'left' monitor? Also, do applications remember which monitor they were last opened on?

That depends on the DE.

On Unity it opens on the monitor you're focusing.

Sometimes it's a bit tricky. Let's say you're focusing on a Window on your main monitor but your mouse cursor is in the secondary monitor. If you hit the meta key, the menu will show on the secondary monitor. Now, if you open an application without using your mouse it'll open on your main monitor, where you had the focused window but if you click on the app it'll open on the secondary monitor because the click changes the focus.

Some stuff is not as polished as it should be but if we take in consideration that Unity has been abandoned for 4 years and before that it wasn't developed at all as all the effort was put into Unity8, I'd say it's a pretty damn good DE.

I hated it when it came out but now I can't live without it.

Two 4k monitors with Ubuntu Mate, works well.

You're talking about connecting an external screen to a laptop or two monitors on a desktop and using it in only-display/only-laptop/mirror/separate screens mode right?

To be fair, my Thinkpad from work is the first laptop that has issues with when (dis)connecting a screen. When disconnecting I need to turn on the laptop screen before disconnecting; for connecting I can usually log in without screen and use Super+P to switch modes and that fixes it.

But other than this first instance, I never heard of this being an issue and people here talk about it as if it's commonplace. I must have used or seen Linux used on at least 30 laptops with 2 (or more) screens without issue in the last ~10 years, counting the ones at my previous employer as one because they were all the same hardware even if people ran different distributions.

Is multi monitor support in Linux broken? I've been going strong for ages with proprietary nvidia drivers and i3/dwm.

I wouldn't say it's broken. But Gnome Shell is made for a single monitor so working with more than one makes it a pain in the ass.

Cinnamon is pretty good.

After trying out a bunch of environments about a year ago, I settled on cinnamon because it had the best multi-monitor support.

Same here with open source drivers and Cinnamon/lightdm.

actually dash-to-dock is working just fine for multiple monitors (and given the strange UI paradigm of Gnome basically a must have). The ubuntu-dock is just a none-configurable version of that. AND in 20.04 the full dash-to-dock just vanished...

Yeah, I had to reinstall one from source. https://github.com/home-sweet-gnome/dash-to-panel