Almost nothing
The short version, which is also the whole version.
This site runs no analytics, sets no tracking cookies, and loads nothing from a third-party CDN. Fonts are self-hosted. There is no consent banner because there is nothing to consent to.
Three things are stored in your browser’s local storage, and they never leave it: your theme choice, your accent choice, and whether you collapsed the sidebar. Clearing site data removes them.
If you send the contact form, the name, email address and message go to Formspree, which relays them to me by email. That is the only data that leaves your browser, and only because you typed it and pressed send. You can email hello@myagwen.com directly instead.
Hosting is Vercel, which keeps standard server request logs. I do not read them, and I cannot tie them to you.