You don't even have to make sure it doesn't exist. There are sometimes reasons for there to be multiple communities serving the same topic and/or audience.
Lemmy.ca's Main Community
Welcome to lemmy.ca's c/main!
Since everyone on lemmy.ca gets subscribed here, this is the place to chat about the goings on at lemmy.ca, support-type items, suggestions, etc.
Announcements can be found at https://lemmy.ca/c/meta
For support related to this instance, use https://lemmy.ca/c/lemmy_ca_support
You can also share your idea and people can tell you if it exists, but regardless you can make the community and run it the way you want
Once you have it set up, you can post on places like [email protected] and [email protected] to help people learn about it
If you don't see what you are looking for make it.
Welcome to our community!
Definitely go ahead and create them, but you'll have to bear the work of bootstrapping those communities until they pick up
If you space your posts and post frequently I'm sure they'll catch on with the default "active" sorting algorithm. You only need a few active members before they show up in the local feed.
Creating them is easy - do it!
Getting them seeded with content and advertising to get some initial momentum to get fresh content coming in? That’s the hard part and I think the reason there are so many gaps.