Click here to see a ChromeUnboxed article from Aug 2021 called "CHROMEBOOKS GAIN CONTINUOUS DICTATION RIGHT FROM THE SHELF WITH CHROME OS 92 UPDATE"
Brief extract ...
"Awesome upgrade to the accessibility tool that is baked directly into the OS. To date it’s only ever been useful for brief periods of activation in order to speak a simple sentence before it toggles itself back off again. Worse still, it couldn’t even be used to speak a search query in your launcher. Needless to say this caused frustration due to its lack of usefulness. However it will now remain ON until the user turns it OFF allowing it to be used for continuous dictation almost anywhere !
There may well be a limit where the time period will eventually deactivate to protect the user’s privacy – say in an instance where someone forgets to turn it off - but as yet there is no specific information about it."