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
magick montage @randomly_ordered_images.txt mosaic.jpg