We have a specific feature that allows you to show and hide all the comments on your cards at once. Here are the steps you need to follow to use this feature:
Step 1. Click on the clockwork icon (settings)
Final Step. Now choose the option “Show/Hide comments”
Note: This option of “Show/Hide comments” is not persisted. In case you log out of the board and log back in, you’ll have to use this feature again.