The square brackets around the hashtags followed by regular brackets and URLs should be interpreted by the client as URLs with link text whatever is in the square brackets - markdown is how it is formatted to do this.

So like:

[#tree](https://pixelfed.social/discover/tags/tree?src=hash) should read #tree in the client.

Strangely, viewing the post here on blahaj.zone, the tree and moss links do display like that, but lichen does not - I suspect because the length of the title (including full URL links) exceeds the allowed title length so it stops parsing the text.