Sorry for posting links to my own comments, but with so many posts for the same problem even a community manager would capitulate.
First: Ready Stickys like this one…
… or look here >> V 1.0.0.5 Can't login and no queue (Switch) - #9 by Geridian-21759
Second: Try this for Offline gaming, should even work on the Switch >> V 1.0.0.5 Can't login and no queue (Switch) - #11 by Geridian-21759
Online mode will not work on the Switch because the Queue patch will arrive sometime later, as the community manager wrote in his blue post = Sticky.
- Actually, Switch gamers are just in the same boat as all console gamers where over the last weekend.
- But now the patch which enables the Switch version to handle queuing is not yet available. If this is due to Blizzard submitting it late to Nintendo or due to Nintendo needing time for testing, only Blizzard knows.
In the meantime, you have a little chance to connect to Online mode on the switch when the login servers for your region have no queue. This could happen when you try to establish a connection to D2R online mode, when not that many gamers try to access the Online mode at the same time as you do.
Greetings from me, a frustrated console player on PS4/PS5.