DGee

I wish there was a way. I posted a request a while back: 
This routine would be a real timesaver in project that have large amount of images of equal quality (and those of differing quality can be corrected manually).

Thanks, I actually compared all sampling options to what photshop does and while I liked the result with Lanczos separable, I found it a bit soft. I didn’t try to use an unsharp mask with it though so I’ll give that a try.
what I did find though is that applying an unsharp mask live filter to the images within Publisher with 0.35 factor and 1px radius in combination with tiff bicubic export renders a pretty much  identical result to what Photoshop does under the hood.

By the way, this recent thread, respectively its posts with sample images about Affinity sharpness in different resample methods on export might interest you, e.g. here …

… or in this post with a more detailed comparison:

Besides applying unsharp mask filter to the image, Lanczos separable has similar result to Photoshop's bicubic.
Because apparently Photoshop applies unshapen mask filter automatically to the image when resizing.
Lanczos sharpen edges of the image. Lanczos non-separable is little too strong on sharpen effect.
So you could do this on export without using a filter.

WOW, thank you so much!
Yea it worked independently from Photo. This should come standard with Publisher, It's ridiculous...
Again, thank you so much, now I just have to figure the equivalent between "Factor" ( affinity) and "Amount" ( Photoshop). 
 
 

If you have Photo installed on the same PC, you can use Photo (by switching to Photo Persona in Publisher) to add an unsharp mask live filter to the images.
This is a manual process per image, independent form export. But once you have a filter layer within the Publisher document, you can copy/move it to any other object, e.g. image frames on master pages. It is possible to double-click on the layer and adjust sharpening settings, too, without leaving Publisher.
Another option would be to batch-process multiple images and apply sharpening with Photo, before importing them to Publisher. If using the same sharpening settings is ok for multiple images.
For simplicity, i attached an otherwise empty file containing a unsharp mask live filter.
Just try to use this, filling in own images and see if it helps. It should work independent from Photo installed on your PC.
Sharpen Publisher.afpub

Serif re-used the poor JPG algorithms used in their legacy programs (The Plus range). I know. I checked. Output is inferior and not optimized for size either. Neither is it an option.
But I can assure you than when it is finally improved you will see release notes and marketing with headlines like "MASSIVELY IMPROVED JPG OUTPUT" 🤨