Let me also list some of the big things that are NOT included:

No Javascript :-) React sites are completely blank, like instagram.com.

No GL/DirectX/Vulkan. It's all software rendered and it just blits a pixel array to screen on every frame. Highly portable though!

Font rendering is antialiased but it's not hinted, and small glyphs at low DPI look start looking blurry.

No Wayland support, only X11 because it's the most widely available. I might do a Wayland port later.

All in one process, one thread per tab. No process isolation (also something to do later)

Only HTTP/1.1 and TLS 1.2, no HTTP2 or later. No IPv6, only IPv4.

No SVG, no <canvas>, no form controls (buttons, etc.), no cookies support (for now...)

The CSS support however is bigger than CSS 2.2: there's var(), --custom-properties, @media queries, etc. and I'm planning to do flex and grid layout too (because Wikipedia uses that a lot).