You can do this as follows (using the same contextual menu button in both cases):
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Starry Night 7 | Multi-Select/Select All from Advanced Find Results.
Right-clicking on the Advanced Find Results produces no context menu on my Windows 10 laptop running SN7. I can search for "Asteroid" and receive a long list that I can "Select All". But Advanced Find seems to have the ability to "Select All" disabled.