The best workaround I found, thanks to Cloph’s help and this thread (in French), is as follows:
1 - Create two page styles:
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“Left illustration page”
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“Right text page”
Assign next style for left illustration page: right text page
Assign next style right text page: left illustration page
2 - Insert a borderless frame in the header of any of the pages with the “left illustration page” style. This frame has to fill the entire page, so that the text written on the right pages jumps directly to the next right page, leaving the left page blank. As this frame is included in the header, it will be part of the page style.
3 - To add illustrations on the left pages: Insert an image in the frame, which is then visible on all left pages → right click on it and anchor it to the page so that it appears only on the desired page.
Another way to do it without inserting it in all pages in the first place is to insert it in a right page, anchor it to the page, cut it and paste it in the left page frame.
There you go! Good enough for the moment, until something more intuitive is implemented!