Hello,
Thank you for contacting Rank Math for help with indexing your images and image sitemaps.
The image sitemap you created with screaming frog should work. Please submit the sitemap into your Google Search Console sitemaps page: https://search.google.com/search-console/sitemaps. Once the image sitemap has been validated within Google Search Console (GSC), It may take a few days to a few weeks for the images to be validated.
Ideally images should be added to the Rank Math post/page sitemaps as shown in the screenshot of your page-sitemap.xml:

Rank Math automatically adds default WordPress galleries and images to the sitemap but cannot detect images that are added within a shortcode. Please contact the Modula gallery plugin to ask if they have a method to add their gallery images to a sitemap. If you manage to add the Modula gallery images to your page sitemap, you can remove the manual image sitemap from GSC and add the page sitemap which will automatically update whenever you add/edit a page.
Hope that helps. Please let us know if you have questions.
Nigel,
thanks for your helpful advice ! Indeed, the sitemap of my website generated by Rank Math displays the few images I have directly placed on the various pages. In other words, Rank Math does the job properly. I already got in touch with the guys from Modula a couple of months ago in order to fix the issue and I only recently discovered that they offer a solution (getting the images indexed) via … a premium price. I am not against premium services, however Seo is first priority.
Best
Olaf
Hello,
We are super happy that your concern has been addressed. If you have any other questions in the future, know that we are here to help you.
If you don’t mind me asking, could you please leave us a review (if you haven’t already) on https://wordpress.org/support/plugin/seo-by-rank-math/reviews/#new-post about your overall experience with Rank Math? We appreciate your time and patience.
If you do have another question in the future, please feel free to create a new forum topic, and it will be our pleasure to assist you again.
Thank you.