You could use a subdomain and host them yourself. That would provide more control an address the GSC issue.
It’s close to impossible to control asset indexing in the the Webflow CDN asset library. No “juice” would flow to you but you can associate the images to your site by including them in a site map. Problem is anyone else could as well.
You would have more control. I prefer to use a subdomain when using a CDN. No guarantees with Google however but at least I can have branding in the URL. Better potential association. It’s what big sites like National Geographic do and for a reason.