Hopefully wayland support will improve
But on my Mac, I use indeed Flameshot, it's not ideal (the window is "shrinking" when a screenshot is captured), but it's better than any alternative I tried.
I'm not affiliated, but the software is simply on a whole different level. They deserve all the fame.
You know Shottr is only available for macOS, don't you? If source code is so important, why do you even bother using macOS?
I wouldn't install Shottr on any of my Linux machines, even if available. Despite it being objectively better than any available alternative. I'd recreate one myself if necessary.
But on a corporate Mac, where 99.999% of executed code is a black box, why bother?