I was asked to show a physical card at the maple leaf lounge in YVR a week ago in order to bring a guest. I tried showing the virtual, but was told flat out you need a physical card. I had an expired one in my bag and showed that which worked.

also, on the star alliance lounge rules page on the web:

“Paid Lounge Membership Customers

As holder of an eligible Paid Lounge Membership, you have access to any Star Alliance member airline’s Business Class Lounge* at the airport where your flight departs. Eligible paid memberships are United Club and Air Canada Maple Leaf Club – Worldwide.

You will need to show your boarding pass for a Star Alliance member airline operated flight together with your valid paid lounge membership card, displaying the Star Alliance Lounge Logo.

You are entitled to bring one guest travelling on any Star Alliance flight departing from the same airport on the same day.”

Based on the rules from the Star Alliance web page, it appears you need a “card”. The real question is - does it have to be a physical or can a virtual card work.