No problem, all feedback anywhere is fine by me :)
The config location, we actually ask libSDL2 where to put the config files, so we're just copying any game that also uses libSDL. Sorry it's not perfect but better than on the desktop :)
libSDL also helps a lot with multi-monitor but it's good to hear that it's working for you. There are a lot of edge cases and we did test for it but only with two monitors.
You're correct, there are a lot of little issues in the menus, I'll add some specific bugs for things we've just overlooked, thanks.
On key bindings, I've added bugs for these, all good points although I'm not sure how to deal with xmodmap mapped keys as SDL (AFAIK) accesses the device directly bypassing any settings. I'll look in to it. Also you found our debug keys and that makes you a very naughty boy! We'll shift them out of the way :)
Fonts: yeah the font is form over function especially for the menus where legibility is paramount. We need to look at that.
Misc: It's a custom engine, the debug menu you are seeing exposes that we use BGFX for rendering and that uses OpenGL2.1 which is old but it also gives us Vulkan, Metal and DX12. We've not enabled those yet as we're trying to focus the testing as we're a two person team, one coder and one artist, and it can get overwhelming very quickly. I really look forward to releasing Vulkan though, it's really nice. THe segfault on exit is completely my fault as I've been too lazy to fix it, sorry.