Arch has an amazing wealth of packages available for almost any type of software between the official repository and the Arch User Repository (AUR).
It couldn't be easier to use either. You install a new Arch package by going to Install > Package in the Omarchy menu (Super + Space) and typing the package you want. It'll automatically fuzzy filter the list of all packages. (You can also do it manually using omarchy pkg add [package] in the terminal).
You can do the same with AUR, just use Install > AUR. Just remember that the AUR isn't vetted by the Arch team. It's like RubyGems or npm. Anyone can upload.
If you want to remove a package, you can use Remove > Package from the Omarchy menu. It'll remove package, config files, and dependencies. (You can also do it manually using omarchy pkg drop [package]).