Step 6 will return you a 404 - comunity non existent if your instance is not federating with the instance of the community you're looking for.
I do:
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Step 1.
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Copy the URL
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In my instance, I use the search fuction. I search for the URL. The community is one result.
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enter the result, the instance has begun federating.
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subscribe.
Not exactly force. It's by design. Instances don't federate with each other unless a user of one wants to communicate with the other (via subscription, or commenting, or whatever).
But instances can block each other and if that happens, there's no way you can access from your instance.
What usually happens is that big instances (like lemmy.ml), just by the mere fact that they are big, are probably already federating with your instance anyway so you may not have encountered this situation.