For the Minecraft Bedrock version provided by Nintendo.

After login on Nintendo Switch account and on Microsoft account, the server tab says "You cannot join cross-platform games without both a Microsoft and Nintendo switch account".

Warning, the main screen before says that I am connected to my Microsoft account, with the ID name. So it is not another duplicate of MCPE-95651

I did not subscribe to "Nintendo Switch Online", if it is that, the sentence should be change to include this name.

Here a workaround that did not work for me : https://answers.microsoft.com/en-us/xbox/forum/all/my-nintendo-switch-on-minecraft-says-you-cannot/4a362f88-2969-4c36-b9e5-31762afa2630 and https://www.reddit.com/r/Minecraft/comments/u1rew7/nintendo_switch_minecraft_server_not_showing/