ports-mgmt synth fails building because its required package misc/ini_file_manager is marked as broken, saying "project files are no longer supported by gnatmake; use gprbuild instead". Bug report for the underlying misc/ini_file_manager problem: bug #278922
As of today, the required package that was failing can be built (see bug #278922). Unfortunately, the build of synth still fails, but at least it's past this particular problem. I'll close this bug report and open a new one regarding the new error trying to build synth.