This URL format with a second hash seems related to unlisted videos.
From what I see there, it doesn’t seem to handle this situation:
~~https://github.com/discourse/onebox/blob/main/lib/onebox/engine/vimeo_onebox.rb~~ It might be a solution to rely on the uri value from the oembed_data output. Even with the video ID only, it gives /videos/795669787:0763fdb816, then you sub : character to /.
EDIT: Sorry did not pay attention I was looking at the old repo