While being decentralized certainly creates a barrier, most of the details behind PageRank (and the other algorithms in use by Google) are pretty well documented. If it doesn’t already, throwing in Lemmy as a keyword should soon bring up a Lemmy intense (probably Lemmy.ml or Lemmy.World) as a top result. As people click those links, the results will go higher.
The bigger challenge is that the content you are trying to find isn’t here yet. Those results on the old site were built over years of massive user engagement. Lemmy has barely had a month since people started joining en masse, and it’s still a fraction of what we lost.
TL;DR: Just keep using it and spread the word. The rest will happen naturally