Many thanks for your attention!Problem had been solved already.
Solution found in:
(after identifying the ‘problem’ in the jicofo log).
I may be mistaken, but think the ‘advice’ in the ‘Advanced configuration’ in the quick install guide is confusing or simply wrong.
I had a completely clean installation (Ubuntu 18.04 - no nginx, no apache2)
Then followed the procedure in the install guide and, later, digital ocean.
So no NAT and no proxy.
Nevertheless followed the tricks in the advanced configuration. No success.
New installation Ubuntu 18.04 (without plesk)
New installation Jitsi
Completely cleaning jicofo log (via: echo > /var/log/jitsi/jicofo.log) - (so you are not confused by the endless log text)
check jicofo log: result: 'Health check failed - too many files open’ (or something like this)
then: systemctl edit jicofo.service (see link above)
and fill in this (new) file with:
[Service] # more threads for this process TasksMax=65000 # allow more open files for this process LimitNPROC=65000 LimitNOFILE=65000
And …. the miracle happens: functions okay.
I afterwards checked the file /etc/systemd/system.conf (according to ‘advanced configuration’)
has not been changed (of course).
Jitsi is a fantastic tool/programme. Deep respect for and gratitude to the creators/developers. Really hope this will be used and installed generally (and we will promote this in EU teacher training https://europeantrainingproviders.eu/meet.php).
So I hope this contribution with help a few people (to avoid my weeks long frustration failing to make this function).
Only thing left: I have the impression that the regular iOS safari browser (in mac mini and mac laptop) has a problem with the video function. App in the iPad tablet is functioning okay. Will check this later again.