You could potentially for every community synced to a subreddit have it redirect to the exact post. I think I saw a website that was tracking reddit to community migrations too. could use that to autoconvert r/<thing> to !c/<thing>@<instance> for you.

On lemmygrad we have that already.

Check your browser of choice. I’m sure there is a URL redirection extension you could install and shouldn’t be that big of an issue to maintain on your own side.

Lemmygrad has a bot that replies with mirrors to posts that contain non-free platforms: https://lemmygrad.ml/u/TankieReplyBot

Here’s the code if you want to run your own: https://gitea.elara.ws/Elara6331/lemmy-reply-bot