You can register .ro domains and every Romanian extension (.com.ro, .info.ro, .org.ro, .store.ro and more), plus international ones such as .com, .net, .org, .e...
You can use a wildcard DNS record, such as *.example.ro, to cover names that are not defined separately in your DNS zone. However, it does not replace the record for the main domain, example.ro, and names already present in the zone may behave differently.
DNS is only part of the setup: your web server or application must also accept those subdomains. For HTTPS access, the certificate must cover the names being used. Check with your hosting provider whether this setup suits your application, then test both an explicitly configured subdomain and a new one.