Camera modelPi cam
**What is the problem?**TouchUI webcam not available
What did you already try to solve it?
Logs (/var/log/webcamd.log, syslog, dmesg, ... no logs, no support)
Additional information about your setup (OctoPrint version, OctoPi version, ...)
Raspberry Pi 4 latest Octoprint and Octopi. Works on Octoprint, but not on touchui
This is expected behavior with the changes to the webcam bits inside OctoPrint and since TouchUI is basically abandoned (with some potential adopters) your best bet is to check to see if anyone has forked that plugin yet to work with 1.9.0.
A warning that it would quit would have been nice before doing the 1.9.0 update.
that's kind of what release notes are for, but as a whole we don't necessarily know which plugins will be impacted, and why we run rc releases for plugin developers to be able to validate ahead of time. your other option would be to downgrade to 1.8.7 OctoPrint.
No one that tested the release candidates said TouchUI was broken... As many plugins as possible are compatible through the compatibility layers, but some do unfortunately slip through.
The TouchUI plugin itself is abandoned and not under development, so until it gets adopted by someone willing to take over then I guess it won't get fixed - unless of course there is definitely a bug in OctoPrint that has made it not work. It's most likely doing some strange things to manipulate the webcam view that don't work with 1.9.0 - we can't guarantee compatibility with stuff outside the API.
just book mark this url on your phone, and you can check the webcam at anytime 
http://octopi.local/webcam/?action=stream
alternatively just get one of the mobile apps for octopi, like for example: "OctoPod" og "Obico"