can one make a collage with Photos

In pages you can add the photos in any manner you'd like. This is a 20 x 30" collage I made with 96 photos:

Just drag the photos to the Pages layout, resize and place where you want them. For this I made a custom page size of 20" x 30".

There's a free app at the App Store that has predefined layouts you an try: Photo Collage Maker - CollageFactory Free on the Mac App Store

Photos does not support colleges. The best you can do is to use the book or calendar projects to arrange several photos on one page, for example a book page with nine photos:

I would use Keynote to arrange photos freely on one slide. Keynote or Pages are now free at the AppStore.

In Photos you would create a book project (it has to have at least 20 pages). Design one page as you like it. Then print the book to PDF and select just the page you want I. the print dialog. You will now have a PDF document with your collage. Open it in Preview and save it as a JPEG or in any format you want.

In Pges you can create a document with just one page and arrange photos you add from the phot browser as you like it.

I created a custom page size, 30" x 20", in the print window. Then I selected that page size in Pages via the File ➙ Page Setup menu option.