Humanius

In the Dutch parliamentary system we do have a two-house structure (i.e. we have a Parliament and a Senate), while also having proportional representation.

• There is a national election every four years that determines the make-up of the national parliament. The result directly proportionally determines the seat division (150 seats total).

• There is also a provincial election every four years. This directly proportionally determines the seat division of the respective provincial houses.
  But it also indirectly determines the make-up of the Senate. The provincial houses hold their own election and vote for the seat division of the Senate (75 seats total for 12 provinces).

It is traditionally seen that Parliament proposes, argues and passes legislation, while the Senate checks the passed legislation for constitutionality before giving it their sign of approval.
Another view is that Parliament is the direct representation of the people, while the Senate is the national representation of the provincial houses.

I think it is worth keeping in mind that an electoral system doesn’t have to be exactly like the theoretically pure version. You can mix and match elements to something that would suit your situation best (for instance in terms of achievability)

To my knowledge Bluesky does not use ActivityPub and is therefore not compatible with Mastodon for federation
They use a different underlying protocol for communication between instances, called AT Protocol

Edit: Different, but not proprietary