My solution for "Webcam Stream Loading" problem (... mostly with Firefox)

Camera model
Camera Logitech C920

Server model
Octoprint & Obico with Debian 11 on Gigabyte Brix GB-BSi5A-6200 8G RAM, formerly Otopi on Raspberry Pi 4 8G

Additional information about your setup (OctoPrint version, OctoPi version, ...)
Tested octorpint version 1.8.3 to 1.8.6

Client
Linux Mint / Ubuntu 22.04 LTS, Firefox, Chromium-Webbroser, Firefox-ESR

What is the problem?
The Webcam Stream preview under the control-tab is black and showing "Webcam Stream Loading", while at the same time the Stream is directly accessible under its port (e.g. http://octoprint.local:8001/?action=stream) but lagging. Also Obico has trouble with the cam.
This happens mostly on Firefox, but also sometimes with Chromium-Browser.
Lagging of the stream and obico trouble are only occurring when the control-tab of the octoprint web interface was/is triggered.

What did you already try to solve it?
First and second page of google search:
Restarting Octoprint, webcam daemon, using another Browser, get some add on, ...

Logs (/var/log/webcamd.log, syslog, dmesg, ... no logs, no support)
Nothing to see there - BUT the Firefox-Console showed some not ending/stopping request

Solution
I deleted from file "OctoPrint/lib/python3.9/site-packages/octoprint/templates/tabs/control.jinja2" all from "{% if enableWebcam %}" to "{% endif %}" and restart octoprint. Voila - webcam-lagging is gone, webcam is still streaming and obico is happy.