https://feddit.online/, the same way https://fedia.io/ does (by the way, Fedia isn’t a software, it’s called Mbin, and doesn’t have such code, so not sure why you’re including them into your title)
https://quokk.au/, it used to be the same when it was still a Lemmy instance
Example of two Piefed instances that currently federate hexbear:
List of Piefed instances that currently defederate hexbear:
https://piefed.fediverse.observer/list
As you can see, instances defederating hexbear are instances managed by teams which were going to do so anyway, as they already did on Lemmy.
Instances who want to federate know how to do so, there are three examples.