How do you add more than 1 song to Photo slideshow?

I've seen this question before, when I searched, but all the answers are old, and I think something has changed.

I never had trouble selecting multiple songs to add to a photo slideshow on my old computer.

I bought a MacBook Air in June 2022.

Now, I'm doing what I've always done, selected the photos, created an album, then created slideshow from that album.

Here is the problem. When selecting songs, it will only let me select one. If I click on another song, it is changing the song you hear, not adding it. I make long slideshows, I usually need 3 or 4 songs.

I have tried double clicking, right clicking, I've searched toolbar for options...

How can I have multiple songs including in a slideshow?

Never had a problem with any of my older Macs!