I tried to get MarkEdit from the Mac App store on my mid-2012 MacBook Pro but:

WE could not complete your purchase.

MarkEdit can't be installed on "Macintosh HD"
because macOS version 12 or later is required.

Alas and alack macOS 12 or later cannot be installed because it's no longer supported by Apple. So the question is, is there a reason MarkEdit cannot be re-compiled to run on the older macOS?