I'll start off
Android 10 oos
Swift installer, swaps themes for desired apps(dark mode for apps), paid
MacroDroid, automated Android-- (does automated functions-move files to "correct folders", free versions allows 6 modules with nearly unlimited functions.
Gravity box for Android 10, allows modifications to the system, free
Microsoft authentication, authentication app for 2 step login, free
Xda labs, obvious but for xda forms, free
Mixplorer - file explorer that has a great ui (I use black/blue theme)
EdXposed, allows tweaks and more, free (removed due to lagged device. Running magisk to run riru, to run edexposed kinda sucks.)
Apps that don't work as intended
Titanium Backup (delete system apps, freeze apps, backup phone info and apps) doesn't delete system apps due to OnePlus file structure.
Swipeback2 (swipe from the edge to go back) caused black screen issues
Edits: added more apps and info