Ideally your link speed would be at least as high as the speed you’re paying your ISP for, if it’s not then you are theoretically not able to fully utilize the bandwidth you’re paying for.

The speed you’re paying your ISP for refers to the connection between the ISP and whatever their demaraction point is at your home, typically this would be their modem.

The link speed you’re seeing here appears to be a WiFi connection between your PC and your router.

Sometimes you have a modem and a router, but it is increasingly common for ISPs to issue modem/router combo units these days (i.e. where a single device both terminates the incoming connection, whether that be DSL, cable, fiber, etc., as well as provides Ethernet and WiFi connections for your devices).

In most cases, you are responsible for all networking beyond the modem/router (which would include the 400 Mb/s link speed you’re seeing here). If possible, it’s always preferable to use hardwired Ethernet since it’s performance and reliability is much better than WiFi.

Troubleshooting WiFi connections is a much deeper topic since there’s so much that goes into it, but in general, you want to make sure that both your devices and your router support the latest WiFi standard, you’re using a channel with the least amount of interference, and you have your router physically located such that it covers the maximum area.

Can you post a screenshot of everything? Can’t tell what the link is. Your PC to the router? Your router to the WAN?