Unfortunately OOTB ServiceNow doesn't offer an easy way to share VTBs with a group. There are a few work arounds you could do however if you need to share it with a large number of people, or want to share it with people as they are added to a group.
This link gives an example of how you can make a flow to add people to a VTB automatically as they are added to a group VTB shared as added to group
Another option, if you have a large group of people to add to a VTB, you can have a platform admin set up an import of users into the <vtb_board_member> table.
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