I have multiple Lemmy accounts on different instances, some of which default to the stock Lemmy client. The accounts that use the stock Lemmy client create the same kind of links to parents of crossposts as Alexandrite. From there, I’m not even aware of a way to link to a post or comment in a generic or indirect way that can be done without knowing the host of the reader who will visit it. I’ve only noticed that links to communties can have a host-neutral syntax. Perhaps the nodes I use that run stock clients are out of date. The latest version I’ve checked this on is 0.19.20.
Worth noting that the smarter behaviour you have experienced may not be related to the OP’s client, but rather your own server or client, and perhaps the software on your side of this does not recognise !zerowaste@slrpnk.net as a subscribed community by which there exists a local copy of posts to replace the link with.