AES-GCM would be very slow on such an old computer, without hardware instructions for AES and for CLMUL.
However, this is precisely the reason why TLS also has the option to use ChaCha20-Poly1305, which will have a decent speed even on an ancient SPARC CPU, though on the most recent CPUs it cannot match the throughput of AES-GCM, which is preferred on these.
So if you want to use a SPARC with TLS 1.3, you must configure it to avoid AES-GCM and use only ChaCha20-Poly1305.