Cannot select "Tile" in Desktop system preference
If your image is larger than the screen's resolution (either by height or width) the ability to tile doesn't work natively.
tldr;

You can trick the option to show by adding an image smaller than your display to the
folder where you're selecting your wallpaper, and then selecting the tile
option.
I'd recommend having a separate folder full of optimised images fit for tiling (they could be copies)

As per above, if the image is larger than the resolution, then My macOS running 10.5.4 is has a display resolution of 2560 x 1600, however is scaled at 1440x900 (image below is a neofetch showing system info)

For an image to be tiled, it needs to be smaller than the width of the display. e.g. let's look at these images. Because the image width is more than my screen, the tile option isn't shown.

However, as is the same with this small image with a width of 900px.

When we reduce the width of the image, we're able to find the average percentage less than the width that would allow for an image to be tiled

At 886 width, we're able to finally select the tile function.
This means that the image width needs to be less than 98.5% of your monitor's width.

You can then select other images with the tiling option, however tiling would look rather odd as by the logic above, the tiling feature attempts to tile an image that's more than the width.

If you've made it this far, I'd suggest having a folder full of optimised images for what you're looking to do. You can resize them in preview as per image below

Hope this helps and explains things a bit!