I have similar issues with a different tool, “Visualisation of compounds”. When asked to produce SVG output, an XML text page is shown (at Galaxy.org). I tried it at Galaxy.eu and it shows the SVG graphics correctly. So the problem may be a more general one not related to specific tools.
The advice from the senior developers is to download the images.
Now, that advice is for one of the public Galaxy servers (ORG), and another does it differently (EU). You could decide to differently for a local server too but I don’t personally know the how-to details. Let’s ask the admins at their chat for help. You're invited to talk on Matrix