The only way I could get this to look better was to open the SVG in Adobe Illustrator and save as... a PDF then open in Affinity Designer.
Even in Adobe Illustrator the image didn't look right with one of the leaves displaying as a dark green brown, I looked through the layers and turned off the offending layers with no adverse affects that I can see. see images below...
Before
After
I think the turned off group is for shading but for some reason when the file is opened it isn't being interpreted correctly.
As a side note and for future reference, it would be courteous to ask the original creator of this image if you could upload this to a public forum. If my solution works for you I would suggest you remove the SVG from this post and I will remove the PDF I have uploaded, I have already deleted the files I have on my iMac.
There is a lot of work in this file and I can appreciate the skills and time invested in creating this image.
Affinity likes PDF files more than SVG. So ask for PDF files instead of SVG in future.
