@Louis-Alexandre there are all good points and I’m curious about your thoughts. For starters, the files are heavy in size because of the best export quality Figma offers. Things like details in shadows, colors etc.
One way to maintain the high quality and reduce the file size would be to include images in the size you intend to have them in your design rather than loading a very big image (pixels wises) and resize it or mask it inside Figma. Anything else requires some form of compression which inevitably reduces the quality — by variable amount but this is whole other topic.
Do you know what your clients see? Is it white pages?
The export window is a great idea but in essence it means that the PDF will be created and appear inside the preview window, which is the same as with exporting the PDF file and opening. I understand a preview window might require less clicks and no context switching, which is useful.
Have you tried the Super PDF plugin? https://www.figma.com/community/plugin/1278730833034634209/super-pdf
It solves the white pages issue, if that’s what you are having. It’s also free and private and exports PDF files in super hight quality.