There seems to be an issue with room settings being ignored by BBB.

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From the reporter:
I'm not sure if this is a Moodle bug or a BigBlueButton bug. Checkout the video which let's me create a room in Moodle with Lock settings applied for Public/Private chat, but when I join the session I'm able to do public/private chat as users. I tried this in 2.4/2.5 with same results from Moodle cloud. Strange!

And yet, BigBlueButton is showing the lock settings, but not applying them.
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This problem needs further investigation as it may be BBB, LB API, or the plugin itself. It may be the way the parameters are passed u overridden, it may be the settings the BBB has at the time of the meeting, it may be the settings Moodle Cloud has by default.

The fist step would be to isolate the problem by testing a stock Moodle 4.0 server with a stock BBB server.