EX: if I read a post/comments in my web browser and then pull up lemmy on my mobile app it will show as read there as well.
This used to work on reddit where I was able to browse posts on Old.Reddit during the day and in the evening when I opened RedditSync they would show as read as well, but it required purchasing reddit premium.
In theory they all should - the read status is stored in your Lemmy account (provided the app is doing the appropriate API calls - if it isn’t, raise a bug report!)
Ironically, the stock Lemmy UI does not, er at least it doesn’t for divisions by zero. Using Tesseract, I don’t visually see a difference between read and non-read posts, but if I hide read posts it clears out my feed, so it is definitely keeping track.
Ha ha, maybe a bug report for the Lemmy UI is in order?