Just for completeness of the thread, the default font stack for $:/themes/tiddlywiki/vanilla/settings/codefontfamily is
"SFMono-Regular",Consolas,"Liberation Mono",Menlo,Courier,monospace
What you describe (Courier being used instead of fallback monospace → Roboto Mono) happens on Chrome and Vivaldi (and so supposedly on all chromium-based Android browsers), but surprisingly not on Firefox. So either the Courier font is built-in into the chromium browsers but not the OS, or Firefox is doing some unexpected interpretation of the font stack and skips the Courier.
I have read somewhere (can’t find it now, but seems true in testing) that the Roboto fonts cannot be indicated explicitly, they only work though the fallback names like monospace. So placing Roboto Mono before Courier, like
"SFMono-Regular",Consolas,"Liberation Mono",Menlo,"Roboto Mono",Courier,monospace
won’t change anything.
I agree that the Roboto Mono is much more readable. Since this applies to the vast majority of Android browsers, I think it would be a good idea to mend it. The only way to do it seems to be removing Courier from the stack completely. So the question remains, with what platform in mind is it there in the first place.
