Server Version#: 1.22.3.4523
Player Version#: Latest Web and Windows Plex App
Smart Collection do not sort by Release Date, however regular Collections do.
Also, I believe Smart Collections are not showing up under the “Related Movies” listed at the bottom of a movie’s details (a movie that is part of a collection), but again regular Collections do.
You need to sort your smart collections during creation or while editing their filters.
The order by release date / alphabetically options don’t apply – from what I understand a future update should clean-up the obsolete option in the advanced tab of smart collections (same for their visibility options)
I was able to figure this out after a small amount of searching, but I’d recommend removing the sorting option from the collection options if it has no effect, or gray it out with a message that says, “Edit your smart collection filter to adjust the sorting order”.