For expressing frustration at the amount of Reddit discussion on Lemmy, I recommend !vent@lemmy.world, !venting@lemmy.ml, or the like.
For discussions concerning Reddit, there are a few different communities you might look to such as !reddit@lemmy.world, !reddit@lemmy.ml, !RedditMigration@kbin.social, and probably others I'm unaware of. The flipside of these suggestions is that these are also the communities those uninterested in the topic may block if they wish to minimize the amount of such discussions they're seeing in their feed.
Constructive threads concerning the transfer of information or app development from Reddit to Lemmy here remain okay, but threads simply complaining will be locked and redirected to the aforementioned venting communities to vent in, or Reddit ones to block to hopefully help curate their feeds.
Thanks for your understanding, and feel free to message me if you need any help in navigating to those communities.