you can check if notify_push usage using following command
occ notify_push:metrics
- Active connections should increase/decrease if NC client is started/stopped
- file change should result in “message send”
- grep your nextcloud.log file for PROPFIND - without notify_push every client performs such operation every 30sec if it works this happens every 5 min (I think)
you can do self test as well
docker exec --user www-data dev-nextcloud-app php occ notify_push:self-test