Yes I believe that is correct emojis are not IDNs; however, ICANN authorizes ccTLDs support emojis separately I think it’s just considered punycode.
Only about a dozen ccTLDs have authorized support for them and allow them to be registered.
Browsers support them, it’s just certain emojis a nearly universally problematic and don’t resolve. Otherwise long as the ccTLD supports DNSSEC the emoji domain names support DNSSEC just the same include those that don’t resolve it browsers.
ICANN rules allow ccTLDs to create emoji/punycode domains - domain registrars and TLD owners are not going rouge and allowing registration of domains in violation of ICANN rules or policies.
Not sure if you know Ben he’s launched a lot of small projects here on HN a few hitting front page and going viral in the HN/product hunt communities, but one of them was Mailoji - basically a cool story of him registering hundreds of single emoji domains and creating email (forwarding) service with them. As one might imagine it didn’t just go viral on HN/product hunt but on TikTok with the kids.
As far as Bluesky they definitely could support emoji domains, I understand the argument that it takes extra effort to do that and they may not see it as worth the time and effort - but I’d be more open minded about the opportunity and appeal to younger users.