So, there are a few different categories of TLDs. com, net, and org are among the original generic TLDs, which had the ideas of being for specific types of site, but in practice have always been available for pretty much any purpose.

Then there are country-code TLDs, your au, ca, and tv domains. In these, the registrar of that particular country sets the rules. au domains require some specific connection to Australia, while Tuvalu has seen it as a good source of income for the country to sell .tv domains to sites that want to have a domain that recognises their primary purpose as relating to video.

In 2012, ICANN opened up the ability to buy new TLDs with almost no restrictions beyond the minimum 3 character length. Though technically com, net, org, etc. are considered generic TLDs, when you see people say gTLD they almost always mean those created under this new scheme. Examples include zone (which my instance runs on), new (owned by Google and restricted to people who use it to perform "new" actions, like Google's own docs.new which creates a new Google Doc), and tokyo (intended for use by things related to Tokyo, but not restricted to such. Other city gTLDs also exist, like melbourne which restricts to businesses and citizens of Victoria). gTLDs are very expensive to create, but whoever owns the gTLD can choose what rules it applies to domains registered under it.

So if you want a domain name that calls to a particular thing, you can find a gTLD that matches that thing and is open for registration for your purpose, or you can spend big to register a gTLD for yourself, or find a ccTLD that's open to those outside the actual country and which fits your purpose.

Mali's a weird one because the reports were that .ml domains not related to Mali were being restricted last year, and fmhy.ml lost their domain over that. So it's weird that lemmy.ml did not.