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.
Yeah, Reaper is surprising! It’s in the Arch repos and Flathub.
I would have been happy if I had to build it from source or download a random deb from their website. But, damn. It’s on Linux and easily installable!