You can browse spartan pages with a Dillo plugin[1], as well as Gopher, Gemini and others.

[1]: https://dillo-browser.github.io/#plugins

> how is it handling modern security features like new versions of TLS or SSL

We support OpenSSL 1.1 and 3 (and any other API-compatible), LibreSSL and mbedTLS 2 and 3. You can choose the one you like/trust more at link time.

> Add support for OpenSSL, LibreSSL and mbed TLS for HTTPS, which is now enabled by default.