This is related to The current Apprise implementation doesn't support attachments · Issue #93993 · home-assistant/core · GitHub
Basically, a while ago @caronc implemented support on Apprise API for attachments, this way you can not only send attachments to services like telegram using telegram:// in apprise but you can relay attachments using apprise:// to another instance of apprise.
This is quite powerful since you can have one central apprise instance with all your notification destinations set and consume that instance from multiple places like Home Assistant, WUD, etc. Having your Telegram / Discord / etc. secrets all in one place.
The problem is, Home Assistant supports apprise, but does not support relaying attachments to apprise. This feature was originally declined due to security concerns that would basically allow apprise to download and attach any local file based on an input URL.
It seems like the Telegram integration currently does exactly that but for some reason Telegram integration attachment was not rejected as a security concern.
Home Assistant should probably normalize this between notifier services, allow attachments on things like apprise like it does for Telegram, and probably some security measure, like a whitelist should be in place for attachments based in internal URLs.