You have to do it to make it easier =>
(only Mac OS X) if (on Windows) install "bash to get it without problems"
1. Collect all your SVG files into one folder
2. Open your terminal =>
go in your folder path with "cd /your/folder/path"
copy all SVG files in only one file width "cat *.svg > index.svg"
!!! Now your SVG coped as "index.svg" !!!
3. Open the index.svg file with a editor =>
change all <svg xmlns="http://www.w3.org/2000/svg" ... > to <g> and </svg> to </g>
write a SVG tag on start <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" ... > and the end of Tag to close the file
open your file on the Browser and check all error and fix it.
It should be look like that =>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="48" height="48" viewBox="0 0 48 48">
<defs>
<path id="a" d="M48 48H0V0h48v48z"/>
</defs>
<clipPath id="b">
<use xlink:href="#a" overflow="visible"/>
</clipPath>
<path clip-path="url(#b)" d="M6 8V2h4v6h6v4h-6v6H6v-6H0V8h6zm6 12v-6h6Vh..."/>
<g>
<path fill="black" d="M8 12H4v28c0 2.21 1.79 4 4 4h28v-4H8V12zm32-8H16c-2.21 0-4 1.79-4 4v24c0 2.21 1.79 4 4 4h..."/>
</g>
<g>
<path fill="black" d="M24 4C12.97 4 4 12.97 4 24s8.97 20 20 20 20-8.97 20-20S35.03 4 h..."/>
</g>
<g>
<path fill="black" d="M38 4H10C7.79 4 6 5.79 6 8v28c0 2.21 1.79 4 4 4h8l6 6 6-6h8c2.21 0 h..."/>
</g>
</svg>
Drag your file in the AffinityDesigner App
Then double click on the layer =>
select all SVGs in the layer =>
Drag it of the assets window in your app
good luck