Hey there, @Peter Straus!

I am not sure what you mean by “tab”? Are you asking how may people can view a Miro board at the same time? If so, a virtually unlimited number of people show be able to access a Miro board as viewers, i.e., not on the board as editors.

As for the maximum number of simultaneous editors on a board, Miro suggests that you keep this number under 300:

Source: https://help.miro.com/hc/en-us/articles/360013912300-How-many-users-can-collaborate-on-a-board-simultaneously

@Peter Straus - Thanks for confirm this - I have updated the title of this post :)

Now, to answer your question: Unfortunately, no, when a user has a card opened/expanded, it becomes locked for all other board participants. I have encountered this scenario myself and it is indeed frustrating.

I have gone ahead and created a Wish List Idea post requesting this functionality - please upvote it and add any comments here → https://community.miro.com/ideas/multiple-user-can-expand-a-card-at-the-same-time-9043

Workaround

As per the Cards Help Center article, it is possible to see some of the Card description/details by zooming in on the Card - more on this here:

💡 The description also becomes partly visible with a triple board zoom. We recommend adding cards with 100% zoom and so if you press "+" in the bottom right corner three times, the card description appears as you zoom in.

Triple zoom

@Marina - Tagging you in here as I see you were the last person to update the Cards Help Center article. Perhaps this limitation can be noted where expanding Cards is noted or in the FAQs?

THANK YOU @Robert Johnson and MIRO COMMUNITY…  YES, it worked--while one person is inside an opened “card”, zooming in to the “card” allowed the other user to access the “expand” function… so simple, but it had alluded us…. to reiterate what discovered: only the first person inside can edit the content…  but just being able to join the first person to view the contents while working together is a big help.