Solutions to stupidly simple problems that took WAY to long to figure out
When installing rofi 1.6.1 from source on Ubuntu, there are some missing dependencies. To install those, enter this command:
sudo apt install libxcb-xkb-dev libxcb-ewmh-dev libxkbcommon-x11-dev libxcb-icccm4-dev libxcb-xinerama0-dev libxcb-xrm-dev build-essential cmake extra-cmake-modules xcb
The check version in the default repos is also outdated, so you need to compile that from source too.
I kinda hate the default Alt+Tab switcher in Pantheon, so I use Rofi to fix that. This is how to use rofi as Alt+Tab switcher. Make sure you have rofi version 1.6.1 installed for this to work propperly.
Create a new scriptfile called alttab.sh with this content:
#!/usr/bin/env bash
xdotool mousemove 960 540 && rofi -no-config -theme alttab -kb-cancel "Alt+Escape,Escape" -kb-accept-entry '!Alt-Tab,!Alt+Down,!Alt+ISO_Left_Tab,!Alt+Up,Return,!Alt+Alt_L' -kb-row-down 'Alt-Tab,Alt+Down,Down,ISO_Left_Tab' -kb-row-up 'Alt+ISO_Left_Tab,Alt+Up,Up' -show window -selected-row 1
exit
Now make it executable:
sudo chmod +x ./alttab.sh
Delete default Alt+Tab shortcut in Switchboard -> Keyboard -> Shortcuts -> Windows
Now link to the file you created earlier and assign it to Alt+Tab.
This looks the best using this custom rofi theme I made: https://github.com/RobinBoers/dotfiles/blob/master/.config/rofi/alttab.rasi