My permissions seem to be reading
root@nooty:/var/run/php# ls -l
total 4
-rw-r--r-- 1 root root 5 Aug 28 16:18 php7.3-fpm.pid
srw-rw---- 1 librenms librenms 0 Aug 28 16:18 php7.3-fpm.sock
these are created when the php7.4-fpm service is running. so …
i got back into /etc/php/7.3/fpm/pool.d/librenms.conf and turned listen-owner and listen-data back to www-data…
and i seem to be getting somewhere now 
(connecting by IP /install.php, it shows more steps - bacck in a bit