Just want to chime in as someone who uses Arch Linux, which is quite similar to Manjaro.
The AUR is considered an “advanced” feature for developers. The community recommendation is to understand how to write a PKGBUILD file before using the AUR - both Arch and Manjaro are very careful to mention that there is no official support for the AUR, and that you’re using it at your own risk. Anyone can upload a package to the AUR, which means it’s quite possible to run into a malicious or just poorly-supported one.
Luckily, there is a brave package in the official Manjaro package repository, which I’d strongly recommend instead of an AUR version. That one is verified to be safe by Manjaro maintainers, will be included in general system updates, and is distributed as a binary so it won’t take several hours to build each time.
It should generally be safe to uninstall and reinstall packages without losing user configurations. Your browser profile is saved in ~/.config/BraveSoftware. I haven’t personally looked at that AUR package to verify that it won’t be removed on uninstall, but you can make a backup of the profile folder just to be 100% sure.
That being said, the AUR can definitely be a great tool if you know how to use it. If you’re interested in any further adventures with the AUR, I would definitely recommend reading the Manjaro AUR wiki page, as well as the PKGBUILD page from the Arch wiki.