It ain’t pretty but this will let you use ImageMagick’s montage command with a random order of images.

First, generate a text file with the image filenames in it, in random order. The sed commands put a " character at the beginning and end of the filename, otherwise ImageMagick freaks out.

ls my-images | \
  shuf | \
  sed 's/^/"/' | \
  sed 's/$/"/' > \
  randomly_ordered_images.txt

Then use that file of filenames as input, using the @ operator.

magick montage @randomly_ordered_images.txt mosaic.jpg