EDIT: seems like BrikoX figured it out, cross-instance searches only work when logged in, I filed a feature request to make this more clear to the user https://github.com/LemmyNet/lemmy-ui/issues/1862

I spun up my own little instance, and I'm able to search for the community from some other instances but not all of them and I don't know why

works: https://programming.dev/search?q=https%3A%2F%2Flemmy.mods4ever.com%2Fc%2Fmeta&type=Communities&listingType=All&page=1&sort=TopAll

fails: https://lemmy.ml/search?q=https%3A%2F%2Flemmy.mods4ever.com%2Fc%2Fmeta&type=Communities&listingType=All&page=1&sort=TopAll

the curl command works fine

curl -H "Accept: application/activity+json" https://lemmy.mods4ever.com/c/meta

maybe Lemmy should dump some debugging info about these searches into the javascript console so we can debug these more easily?