In the 'Wednesday 2nd August' post on !trendingcommunities@feddit.nl there's a few complaints about how the links don't open in Sync.

It looks like Sync only supports the '!' method of providing relative links, and not the [Link](/c/community@instance) method. It's the other way around for at least one of the other mobile apps (Jerboa, I think)

I've decided this is a Sync problem, but if that's an unpopular opinion and it's not something that the Devs feel the need to fix, then - if you really want to use a Community like trendingcommunities - the source for bot is available (see the sidebar), and it may well be that someone needs to create a alternative community with posts in the alternative format.