Please note that for the above links to work, someone on your instance needs to have already subscribed to or searched for the remote community so it populates on your instance. You can search in Communities > All for [email protected], as an example, and then the links should work after a few seconds.
This site is a great resource for finding communities.
It looks like there are several that are already quite large:
cybersecurity (697 users)
securitynews (587 users)
Please note that for the above links to work, someone on your instance needs to have already subscribed to or searched for the remote community so it populates on your instance. You can search in Communities > All for [email protected], as an example, and then the links should work after a few seconds.
https://lemmyverse.net/communities is also great from browsing communities.