ChatGPT and I came up with this bookmarklet which I'm using until this is resolved.

You set your home instance, then just click it when on a post on another instance. It grabs the post title and the author, redirects to a post search of the title on your home instance, and copies the author to your clipboard to Ctrl-F if there are too many results.

You have to be pretty quick on the draw to be able to enable clipboard access when using it on a new instance for the first time. So it's like a game, too.

javascript:(function(){
  let instance = "lemm.ee";
  const personListing = document.querySelector('.person-listing');
  const author = personListing.getAttribute('title');
  navigator.clipboard.writeText(author);
  alert("Post author copied to clipboard.\n\nCtrl-F + Crtl-V when redirected, if necessary.");
  var title = document.title;
  var lastDashIndex = title.lastIndexOf(" - ");
  if (lastDashIndex !== -1) {
    title = title.substr(0, lastDashIndex);
  }
  var encodedTitle = encodeURIComponent(title);
  let search = "https://" + instance + "/search?q=" + encodedTitle + "&type=Posts";
  window.location.href = search
})();

I always check who I’m replying to, and make sure the link is relevant to them.

Then also add the home link below. It can be quite a bit of work.

Both are unique URL, and post ID, so it’s not as simple as adding and @mydomain like sharing a community or user.

So A won’t really work. But B would be a cool option for future development.

I use this universal link switcher userscript.