For example, this invidious instance offers a download option for a YoutTube video, as that instance does for all YT videos:
https://invidious.fdn.fr/watch?v=lU4vv7qCQvg
Exceptionally, if you opt to download it it merely opens a player to watch realtime. While other downloads from the same invidious instance have no issues. Why is this one getting different treatment?
Try right clicking and “save as”? On mobile Safari it pops up with view and download as options.