@Maria Tahri - Here’s a trick for you.

Shift + drag over a number of items should show you a count of the objects selected, except when they are all the same type of objects. So, the workaround is to add at least one other item type into the selection and then click on the filter to see the count of all object types.

In this example, there are 15 branches on the mind map. When I Shift + drag to select them all, I don’t see a count, but if I add a sticky note and do it again, I can see that  there are 16 objects and click on filter to see a breakdown: