For me, it was perhaps simple-scan, a very simple and efficient GUI to scan documents. I used it with my Brother printer / scanner and it works like a charm. Especially since I do not scan stuff often, so a program with more complex UI would have the effect that I forget how to use it until the next time.
Reaper is like the Arch Linux of DAWs. It’s power is in its flexibility and customization. That said, I found it to be uninspiring in its complexity out of the box. That said, the Reaper community is amazing. If you want to mod and customize it into your ideal DAW,y recommendation is to hit the community forums, Discord, etc.
Personally, I bounced from Reaper almost instantly in favor of Bitwig and Renoise on Linux.