Good news! I think I found what the problem was and a workaround for it. I was using an older version of macos before but upgraded recently to the latest and got this issues back again. This time I thought I should investigate it a little further. I started suspecting it had something to do with accessing the global folder "/usr/local/share/frobtads/tads3/" and it turned out that was right. If you for instance do a clean copy of the whole tads3 folder just mentioned to your home folder and then prefix all your search paths in your Makefile.t3m file with /Users//tads3, e.g:
then the compile issues will go away! (At least they did on my machine.)
I’m guessing this has to do with some level up in security aspects of accessing folders from applications that’s been introduced in newer MacOS versions.
Please let me know if it works out for you too.