Maybe Duck-Duck-Go need to have a !bang search modifier for Lemmy. https://duckduckgo.com/bangs
Most likely not feasible, because what the bangs do is passing site:domain.com
to the search result. As you know, Lemmy does not have a singular domain name so this won't work for it. As a matter of fact, there is a bang for Mastodon, but it only searches the biggest instance, mastodon.social.
There is currently a pending feature request to add a feature dubbed “multireddit” that communities can add themselves to and where the end user would only have to sub to one multireddit to have access to all the communities with the same on multiple servers. It seems to be opt-in for communities, though, which is good IMO.