This also started happening to me once I updated to 1.17.0. I tried to connect to all of the servers in the list, only to be shown the 'Unable to connect to world.' screen.
Edit: While playing on a survival world, I got a message in the top-right corner (this is part of the Switch's UI) saying 'Server Maintenance Started'. I was able to join servers after that.
RGames Offical
This also started happening to me once I updated to 1.17.0. I tried to connect to all of the servers in the list, only to be shown the 'Unable to connect to world.' screen.
Edit: While playing on a survival world, I got a message in the top-right corner (this is part of the Switch's UI) saying 'Server Maintenance Started'. I was able to join servers after that.