Highlights include Sliding Sync (instant login/launch/sync), Native OIDC (industry-standard authentication), Native Group VoIP (end-to-end encrypted large-scale voice & video conferencing) and Faster Joins (lazy-loading room state when your server joins a room).
I found this if it’s what you mean, but all it mentions tech-wise is that Lemmy is slow to develop. This does make sense, is it what you’re referring to?