I can't access the marketplace or edit my characters on my Nintendo Switch

I haven't been able to connect to the marketplace on my Nintendo Switch for the last four months and it either says "Invalid session (Try restarting your game)", "We're having trouble connecting to the Marketplace right now. Please try again later!" or "Error code - ..."

 

I also haven't been able to edit my characters for the last four months because I can't interact with the "Edit character" button and it just goes dark grey.