DOH! Figured it out - it was my own stupid fault. In config.php php_executable was set to the system php, rather than the brew one. It caught me out because I was assuming that the php used would be the same as the one I set in apache, which is why info.php looked fine but I was still having issues. So in case anyone else has the same issue, in config.php change:
This maybe very that’s my config on Synology specific:
With PHP 7.2.13, intl 1.1.0, icu 56.1 tt-rss update missed the Uconverter class.
Digging in my config I found a mismatch between PHP_EXECUTABLE (pointed to an also existing 7.0 binary) and the one used by the web server (7.2), setting PHP_EXECUTABLE to PHP_BINARY solved this issue immediately.
In my case, the issue wasn’t that the intl module wasn’t installed, but rather that it wasn’t enabled. So if anyone else is still stuck after installing the package, make sure you have extension=intl in your php.ini.