Newly created cards not showing in the browser

I am using Anki 2.1.15 on Linux Mint 19.3. I am trying to add new cards. However, when I click on the Add button in the Add windows the new card is NOT added. Updating the browser does not add the card to the browser. Closing the browser and reopening does not show it. Going to the main Anki window and chosing Tools - Check Database does not fix the problem. When I seach on the net all I get are questions about newly created cards not showing when studying the deck. Can anyone point me in the good direction?

Check the Default deck ?
Try to add a Note in the Browse screen.

trying to create a new card in the default deck is one of the many things I’ve tried. On the other hand, I’ve never tried to add a note in the browser. Thank you for that idea.
Happily and frustratingly, since my original post, the problem has resolved itself after almost six hours of crashing about and I have no idea why. Nor any idea how to recreate the problem.

I would mark the question closed, but I don’t know how. Again, Vit, thank you for your answer.