Hi Peter,
All working again on my MacBook Air - many thanks.
Not really a surprise that it was not a network, Beta, router, problem as Qobuz was running perfectly and Tidal Connect and the Lumin app were both delivering content without a hitch!
The only logical answer was a Tidal problem within Roon!
I could easily have wasted an extra couple of days, in addition to the frustration and time already spent, trying to roll back to a previous version of MacOS and various other things without any likelihood of a solution or help from Roon support.
So, many thanks again.
Best
@MaxH13 I assume you did the above and Roon Tidal is now working? Any additional steps did you take?
No additional steps.
Uninstalled Roon and anything in the Library with a Roon folder/filename.
Reinstalled Roon and Bridge.
Logged out of Roon on the desktop and changed Core to MacBook Air.
Simple 
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