Aside from obtaining those free subdomain names from co.cc, co.nr which doesn't look good for me, there are also some GPTs which offer free domain names, although you have to complete some offers and these kind of GPTs usually doesn't work for international members.

So have a look at domainlagoon.com. Although, again international members can only earn here by referring other tier1 members.

Also, free webhosting sites usually offer free subdomains too.