Do not serve SVG images in email content
Turns out that even with modern email we cannot rely on SVG file support.
The Google image proxy that every image gets served by when mail is processed through Gmail will not serve your SVG content.
This is a long standing issue and apparently will not be fixed.
You can possibly use inline SVG or a failover via the image tags src & srcset attributes, however, just converting to PNG/JPG will end up being the least problematic.