Writeup from 2022 that I assume is mostly still valid. TLDR:

1. Mainstream Linux is less secure than macOS, Windows, and ChromeOS. (Elsewhere: “[iOS/Android] were designed with security as a foundational component. They were built with sandboxing, verified boot, modern exploit mitigations and more from the start. As such, they are far more locked down than other platforms and significantly more resistant to attacks.”)
2. Move as much activity outside the core maximum privilege OS as possible.
3. OP doesn’t mention immutable OS, but I assume they help a lot.
4. Create a threat model and use it to guide your time and money investments in secure computing.

Once you have hardened the system as much as you can, you should follow good privacy and security practices:

1. Disable or remove things you don’t need to minimise attack surface.
2. Stay updated. Configure a cron job or init script to update your system daily.
3. Don’t leak any information about you or your system, no matter how minor it may seem.
4. Follow general security and privacy advice.