Posts and comments have yet to be implemented in this way, but instance-agnostic links already work for communities. Simply typing !memes@lemmy.ml or !bicycles@lemmy.ca or whatever will give you a link which redirects users to that page on their instance. Your instance might have to be running the latest Lemmy version, though.
What are you entering in the search bar?
Either paste the full URL (https://reddthat.com/c/rts) or write !rts@reddthat.com. You might need to click the next & prev buttons a couple of times for it to show up, especially for smaller communities.