@Gotterdammerung @rolle That's sadly due to CORS, and I can't do anything about it. You would need to contact your instance admin and have them allow anonymous cross origin on the server that serves the media for your Mastodon instance.
A workaround could be to look up your profile on an another instance, and use that instance's link to the tool 🤷
Like this:
https://mementomori.social/@Gotterdammerung@glitch.social/110677108790619423