It's extending the signal from GL-MT3000, which is running VPN and AdGuard Home, and as you can see below, the CPU Average Load is very low (as expected):
This phenomenon has been reported by other users.
This is a normal behavior on B3000, which may be as the network packets is not accelerated through hardware, resulting in CPU processing.
As long as it does not affect the normal use of the router, it can be ignored, the top actually sees that CPU and memory usage is normal.