Ah, it’s because nobody on your instance is currently involved in that community, so it hasn’t been federated to Beehaw yet. To fix that, go to the search tool, make sure that you have “All” selected for all four filters, and enter “https://lemmy.world/c/ece”. If you get a community result, you can click on it and subscribe to the community and then crossposting should work. If you get too many results, try switching the scope from “All” to “Local”. If you get no results, it means that federation is pending but delayed. Give it a minute or two and try the search again; eventually the community should show up.
Oh, yep, you’re right. As I stopgap, if you’d like, I can crosspost for you, so at least you can watch for answers at !ece@lemmy.world in a browser. Just let me know if I should do that.