Mojang Studios Note
This should now have been fixed. It was caused by expired Xbox tokens which was not properly refreshing. If you are still experiencing this issue please report a new bug.
Potential Workaround
Sign out of your Microsoft account on the launcher and sign back in. If this doesn't fix it do the following: Uninstall the game via your PC's "Control Panel" by going to "Programs and Features", and reinstall the launcher and game via https://www.minecraftdungeons.net/en-us/download/
Note: This should not delete your characters. However, in case you're running an older version, you can backup your saves before reinstalling.
The bug:
Upon starting the launcher, the launcher will state that it is unable to verify what products/DLC you own and to check your internet connection (the connection is fine). The game is still able to start and any DLC content you own will be usable in-game.
How to reproduce:
1. Start up the launcher
2. The launcher will state that it cannot verify what products you own.
I am so relieved to see that this issue is finally being worked on. Thank you to those on the team who have picked this up