Hmm, that’s odd. I should say now that I’m a general user, not a tech wizard, so I may not be able to help any further.
Could you give some examples of diaspora* posts containing videos that auto-play when you scroll? In my experience, embedded videos from YouTube, Vimeo and so on don’t auto-play in diaspora*. It’s quite possible that you don’t see the ‘block’ icon in the address bar because there are no videos trying to auto-play. Try the example page used in that instruction: https://www.bbc.com/reel/ I’ve just tried that and the icon appears, and I’m able to choose my auto-play options for that site.
On GIFs, at the risk of stating the obvious, you did enter ‘none’ (all lower case) rather than ‘None’ (as you said above), didn’t you? If you correctly set ‘none’, it should definitely have worked, because I’ve used it myself in the past. Try toggling the settings: find a GIF in a diaspora* post or other web page, set ‘once’
Long posts should be auto-hidden behind the ‘show more’ shield; the problem is with posts whose length is mostly due to embedded images, as this doesn’t always trigger that shield, which is what I tried to explain.
As to liking, that is considered an ‘interaction’ that signals an interest in interacting with that post. That’s why you’re subscribed. While it would be useful to have a setting, from my point of view it’s a very good argument against indiscriminate use of the ‘like’ function; if you don’t want to interact further on that content, don’t ‘like’ it. Failing that, just click bell icon if you don’t want to interact further. (Also keep in mind that every time you ‘like’ a post, the person who posted it gets a notification that you have ‘liked’ it. There is nothing they can do either to (a) prevent anyone from ‘liking’ their post nor (b) getting a notification every time someone does ‘like’ that post. For some people, myself included, that is extremely annoying. That’s another good reason to limit the use of ‘likes’ to when it’s really needed.
As I say, I’m not an expert, just another user who’s tried to deal with these things myself in the past. I hope I’ve been able to help; if not, someone should be along soonish who can.