For instance I know i can navigate to https://lemmy.ml/c/daystrominstitute@startrek.website to see the “daystrominstitute” community at startrek.website, but is there a way where I can see all (or even just the most popular) communites at startrek.website, while still logged into my lemmy.ml instance (so i can just hit the subscribe button if i want to join)?
Try https://lemmyverse.net/communities
If you set your home instance, all the links for communities will take you to your instance’s version of that comm.