Onion services can only use a single TLD (.onion). The Tor network is designed to use only one TLD and you would need to modify all Tor clients and servers if you wanted to support more.
As the address space for onion addresses will never run out and addresses are not human-readable, there's no practical need for additional TLDs. Multiple TLDs for onion services would also harm usability as it would be more difficult for users to know if they're connecting to an onion service or a regular DNS-based address. The '.onion' TLD is the only Tor-related TLD officially recognized by ICANN, and I think it would be unlikely that they would recognize others without a good reason.
In addition, the Tor Project also gives .tor.onion addresses to special organizations such as The Intercept for their Secure Drop instance (theintercept.securedrop.tor.onion), but this is in testing and is not available to regular people.
To summarize, there is only a single TLD for onion services and if you wanted more, you would need to convince the Tor Project to build support for it, which would be very unlikely.