For example, suppose you click: communities » All and then query:
tech -site:lemmy.world
in the world of web searches, that would look for “tech” but it would exclude results on lemmy.world. I see no way to do this. In general, there are certain instances that folks might prefer to avoid. Seeing an imbalanced ocean of links flooding in from a giant node isn’t useful if we are actually looking for less central communities.
not sure if it is helpful to you, but you can block whole community in your settings > blocks
doing it just for the search could be workaround if you have just one or two specific communities that clog your results