With mkp find one can list all unpackaged files in a site.
Whenever there are already extension packages installed these also get listed in the output of mkp find:
File Package Version Part Mode
-------------------------------------------------------------------------------------- ------- ------- --------- ----------
getservices.py Binaries -rwx------
$OMD_ROOT/local/share/check_mk/enabled_packages/check_by_ssh-3.0.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/dovereplstat-4.3.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/icpraid-5.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/gamatronic-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/mk_filehandler_bakery-0.3.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/postfix_mailq_details-5.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/postconf-5.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/check_restapi-0.4.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/cachet_alert-2.1.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/virtuozzo_vstorage-0.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/wireguard-1.5.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/dell_omsa-3.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ox_filestore-4.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/ecallch-2.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/aspsms-1.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ricoh_used-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/openvpn_clients-0.4.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/entropy_avail-5.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/cpufreq-2.3.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/kentix_devices-3.0.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/hwg_wld-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/sslcertificates-8.7.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/apcaccess-5.2.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/rspamd-1.4.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ups_alarms-1.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/check_mk_api-4.0.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ups_out_source-1.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/proxmox_provisioned-1.3.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/velocloud-1.4.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/dell_sc-3.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/msexch_database_size-1.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/usp_ses-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/memcached-5.6.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ecityruf-0.3.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/fastlta-0.1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/imap-3.0.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/stonesoft_firewall-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/heinlein_inventory-2.1.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/amavis-6.1.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/dir_size-5.2.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/siproxd_stats-0.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/data2label-2.3.0.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/check_snmp_metric-0.4.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/dirvish-4.1.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/mailman_queues-5.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/netpdu-0.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/ox_runtimestats-6.4.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/check_calculate-0.2.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/lvm_cache-0.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/check_snmp-0.5.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/ceph-11.18.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/carel_sensors_lcp-1.1.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/enexus-0.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/lsbrelease-5.7.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/bi_aggr_metric-0.1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/infortrend-4.5.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/wagner_racksens2-2.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/otrs-6.1.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/netifaces-7.0.1.mkp -rw-------
$OMD_ROOT/local/share/check_mk/enabled_packages/updater_hostname-1.2.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/if_avg_metrics-0.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/acgateway-1.1.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/dell_os10_chassis-1.0.mkp -rw-rw----
$OMD_ROOT/local/share/check_mk/enabled_packages/hpsa-8.4.mkp -rw-rw----
IMHO this is not necessary.
An improvement would be to sort the output.