I have a question about the installation. Could this erratic behavior be a result of this .sdk file being installed in the wrong order? is it possible to uninstall Frescobaldi using some magic formula like "sudo port uninstall frescobaldi" and do an install again so that the installer finds the sdk file. Especially will there be a difference. Just an idea...
Well, it’s unlikely. I happen to have frescobaldi installed via a fresh new MacPort procedure (after upgrading to MacOs Monterey) just last week and the missing sdk message I encountered was related to all the qt5 stuff that frescobaldi needed in order to be built. You were lucky it was not a stopper as it was in my case: I had to manually add `use_xcode yes` in the corresponding PortFile of py310-poppler-qt5 in order to make it build properly. Perhaps it has since been corrected so that if the «standard» way for qt5 to find the sdk won't work, they try the `use_xcode yes` trick (whatever it does) before giving up.
All these problems, even if triggered during frescobaldi install, are unrelated to it. That's just the way Macport is doing the job: whenever you add a package to MacPort, it asks you what should be present on the machine to make your app work and then try to install it by itself, saving the user the trouble to install all the extensions and preventing multiple installs of the same tools whenever two different packages need the same first building block.
But as a matter of fact, it won't help to uninstall frescobaldi to try to correct for lilypond path (as for one reason is that MacPort don't throw away uninstalled port but keep them somewhere, ready to reinstall it without further building in case you change your mind). I would rather suspect that the search for different lilypond locations was done after you first looked there (perhaps triggered by one of your tinkering), was written down somewhere so that the next frescobaldi startup shows it.
Happy that you finally managed to get it work and have fun coding with lily on frescobaldi !