I have a lemmy account on lemmy.sdf.org

When searching for communities to join I can see several in the list from lemmy.ml and beehaw.org

but while searching for some communities that I know exist on lemmy.ml or beehaw.org I am getting no results

will a community from instance A only appear in search results on instance B if a user from instance B has already manually subscribed to that specific community from instance A?

basically, there is no scraping of ‘all available’ communities even when two instances know of each others existence? only ‘specific communities’ are indexed when a user has manually found/subscribed?