Image size in block gallery (5.2.7)

Hi team,

Run a WP 5.2.7. Is there any way to simply add “image size” option for block gallery : by example adding a short code in the function.php theme. It’s already there for simple image block.

This feature exists for gallery in later version (by example 5.4.8), but would like to add it withtout doing a major upgrade since the website and its shop are perfectly running.

On this link a screenshot of 2 gallery block options from a WP 5.4.8 and 5.2.7 :
https://www.zupimages.net/viewer.php?id=21/51/4bmd.jpg

Thanks a lot for reading