A CSS script could do that... if the :has() selector is supported.
With that said, I've recently run into issues with that selector not being supported (due to it being recent CSS spec) in two different (but not recently updated) user style extensions that I've tried it with (in one, it is entirely unrecognized; in the other, you get errors when trying to do nontrivial things in the :has() ).
I could copy/paste some example user CSS for you if you'd like to see if you can get it working.
The first part prepends a red heart to usernames from a particular remote server (and variants of the CSS selector can be copy/pasted into a comma delimited list to allow the rule to apply to other servers as well).
The second part prepends a yellow star to usernames from the local server... by crudely assuming that they won't contain any periods (CSS selectors aren't flexible enough for anything more elegant). The selector can instead be applied to the first rule to make those hearts as well.
I whipped up a proof-of-concept user CSS that does this (and should automatically adapt to entries shifting down).
**********
@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("pawb.social") {
a.text-info[title$="@lemmy.blahaj.zone"] span::before {
content: "❤ ";
color: red !important;
}
a.text-info:not([title*="."]) span::before {
content: "★ ";
color: yellow !important;
}
}
@Wander A more quality (but more labor intensive) solution would be to have an account setting that toggles a short CSS file containing overriding CSS for the adult image blur. This way, users could choose to have or not have that blur regardless of which theme they chose (without having to have two separate copies of each main CSS theme to achieve that).
Peertube might be an option; it's basically an ActivityPub server that's intended for video and stream hosting, by my understanding.
I can confirm both that my original version has the bug you described and that your fix does not produce that bug.
I don't actually have a native Lemmy account, so I didn't realize that upvoting would cause the upvote count to gain a CSS class that I used in my selector.
(Thankfully, the DOM changed to reflect given/taken upvotes in spite of me not being logged into the Lemmy server at all; I only got a "Not logged in." error each time.)