I have tested this on the new rc build 0.99.135.0.1-rc (WebKit 622.1.15.19.2), but unfortunately, it still doesn't work. Seeing that the webkit version didn't change, it supports @laiz suspicion that this is related to webkit.
I have found a way to to reproduce this in controlled environment. I am adding the info here, so you can create test case based on this if you want.
In short, I think the data:text/calendar links don't work in Orion.
See ics download link in this chatgpt generated test. It works on Safari, but doesn't on Orion.
