Is this a good upgrade from an older Wi-Fi 5 router?

Yes, if your devices support Wi-Fi 6. It adds the newer standard and four streams, which helps with many devices at once. Older Wi-Fi 5 devices still connect but won't see the full benefit.

Does it work as a mesh system?

No. It is a standalone router with no mesh support, so it cannot be paired with mesh nodes to extend coverage. For a large home, a mesh kit is the better fit.

Can I connect a printer or hard drive by USB?

No. There is no USB port, so storage and USB printers cannot be shared through the router. Wired devices connect through the four Gigabit LAN ports.

Does it have a built-in modem?

No. It has one WAN port and no xDSL modem, so it needs a separate modem or an Ethernet feed from your provider.

How many wired devices can I plug in?

Four, through the Gigabit LAN ports, plus the WAN port for the internet connection. All LAN ports run at Gigabit speed.

Is it good for a large house?

It is best for apartments and small homes where one unit covers the space. With no mesh support, a large multi-floor home will likely have weak spots.