Very similar to what I was looking for as well! I have to resize images for our photo club site. In Photoshop I have an action that will resize the width to 600px and the height will scale appropriately then add a square frame in white around the entire image. I Affinity the macro will do all that except the height will be the same as the image I used to create the macro - throwing off the dimensions!
Image 1: Original 8x10 test image.
Image 2: after resizing and adding border (recorded this as a macro)
Image 3: Image 2 with border added to show the result more clearly.
Image 4: Image 3 after macro was run. The entire image is square as it should be but it has resized the original square to 8x10 ratio.
However, the batch processing to resize works perfectly! Maybe I can combine that with a macro?