Were those websites supporting SSL connections, much less TLS 1.2? That would be my question on hardware that old. (In this case, it looks like they offload TLS to Cloudflare, so the machine itself isn't doing any encryption/decryption.)
He offloads TLS to the Proxmox server within their home network. TLS is used between that server and Cloudflare to keep everything safe during transport.
The question is more about the hardware. Back then, TLS existed but was used sparingly for things like banking, because of the computational overhead, at both the server and client end. Today's computers are so much faster that we don't even think about it.
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.
Typically, fun memory they'd move to a secure connection for credit card input, but most of the site would be open HTTP - why secure what isn't confidential? Concerns about 3rd parties eavesdropping on the sites you visited weren't a big thing at the turn of the century.
