Unfortunately the way federation works, if nobody from your instance had previously subscribed to this community, the comments won't be fetched when you subscribe.

You'll be able to see the comments on any instance that was federated here at the time the comment was made.

So my home instance: https://aussie.zone/post/407650

Or the ttrpg.network: https://ttrpg.network/post/102392

Will both work. As will any instance where someone has been a subscriber here for a while. But it looks like not your instance. Here's some advice if you want to interact with the comment after reading it on another instance.