Currently the workaround to invite users from Team B to a board within Project A on Team A is to invite the users of Team B to the board in question by individual email invite after exporting all users within the Miro company. While I am able to script using csv exports, this does not make board management and the permissions within them scalable. It’s just bad. Also, if you filter the list of users from the Admin page for users, and filter to the Team you wanted and then export - it does not export that filtered list, it exports the entire company list. The filter does nothing but display who is in that filter in the viewspace below.
If Team A contains 200 people today, and 300 people on January 1st. 100 users will need to be invited to that board/project specifically between the two dates. Instead, if Teams are able to be granted access to Boards/Projects, there is no need for anything to be modified, as the Team has already been granted access to the Board/Project in question.
If you want to extract all the emailed users from a .csv file of your company, you can use the powershell script below.
Import-Csv '.\path\to\file.csv' | Where-Object { $_.'ColumnName' -match 'StringToMatch' } | select E-Mail
I do not understand why Miro does not have the ability to add different Teams to boards or projects within other Team spaces.

