You can join any lemmy and still interact with the others. Lemmy.ml does not require an email but you have to answer a questionnaire and wait to get approved. I got approved after a few minutes. The site is pretty overloaded now and some people are running into problems making accounts. lemmy.world requires an email, but you can use a temporary email and there's no questionnaire. Here's a list of federated lemmy sites https://the-federation.info/platform/73. Be wary of beehaw.org, they have some sketchy lib mods who have already blocked hexbear as a hatespeech site, which is unfounded to the point of absurdity. I would steer clear of associating your account with them, although it probably doesn't matter.

so, iirc, during account creation lemmy.ml has you answer three questions, which I think were:

• why do you want to join lemmy?
• what communities do you want to join?
• why did you choose this username?

my responses (which you can probably get away with paraphrasing) were something like:

• "i like the idea of a social network with no owners or venture capital calling the shots and shaping discourse"
• (i just glanced at the community list and named a few I liked, including /c/socialism, /c/china, and like /c/music)
• "[username] is already my username on another leftist forum that will probably federate with lemmy in the future"