I currently use Swiftly Switch. It is an app that adds a small bar to the side of the device and by swiping that part, I am shown a list of apps of my choosing. This allows me to open apps much faster.
Sadly, it is not open source. Is there something similar but open source?
I've had something similar on MIUI for a while, but you had me curious because I remembered I used to use this Taskbar app in the past and it turns out it's actually open sourceand on F-droid! It seems to fit your description more or less
I just tested it and, sadly, it is not quite what I want... Its UI/UX is not quite there yet.. Maybe I will do some feature requests in their repo.. But as it is it doesn't replace Swiftly Switch.
May I ask what you are using on MIUI? I am also on MIUI!