He mentioned it in his “Apollo will close down on June 30th” post on /r/ApolloApp (I’m linking it here, but here’s the quote so you don’t have to gift Reddit your traffic):

Will you build a competitor? Move to one of the existing alternatives?

I’ve received so many messages of kind people offering to work with me to build a competitor to Reddit, and while I’m very flattered, that’s not something I’m interested in doing. I’m a product guy, I like building fun apps for people to use, and I’m just not personally interested in something more managerial.

These last several months have also been incredibly exhausting and mentally draining, I don’t have it in me to engage in something so enormous.

I think Christian mentioned he isn’t planning to port Apollo to Lemmy, but I haven’t given up hope just yet!