At the risk of sounding stupid giving a serious answer to a joke question; I don't know the details but lemmy might not work, because the 3DS doesn't support the ciphers lemmy uses. Other sites might work, because they support older ciphers for backwards compatibility.
A reason why lemmy might not want to support those is, that it could give attackers an opportunity to "hijack" your login because they can decrypt what you're sending to lemmy.
If you just wanna browse lemmy anonymously tho, you should be able to do that, yes