It finally fails, sort of, under Sonoma :-( What happens is that the main window, and several of the inspectors, have an odd vignette around them. It's still possible to use it in a rather crippled way. At least you can do some limited editing and export, print, etc.
Eazydraw is the best alternative I've found so far. It imports Intaglio perfectly. While it's shortcut keys are different, it does have the ability to edit them. If someone wants them, email me (gwj at me dot com) and I can send you my Menu Keys and Quick Keys files, which you can import from the Eazydraw menu. Then it's pretty darned close for common things. Their support is good via email and they have a good manual etc. Also you can edit does on your iPhone and iPad, and it also runs under Windows. So that's where I've moved...
There are also some free viewers and editors for SVG files, a kind of XML, which is what Intaglio is based on.
-Gary