The Laptop Uses the 802.11b/g NIC. How Can I Associate It with a 802.11n AP?
You can associate it with 802.11n AP if the AP does not set the 802.11n-only mode. However, the signal transmission rate of the APs in 802.11b mode is low. In contrast, the time that the 802.11n APs take to transmit radio signals at 300 Mbit/s accounts for only 1/27 of the time that the 802.11b APs take to transmit radio signals. Therefore, when a comparatively large number of old wireless terminals are connected to the 802.11n APs, the AP performance decreases considerably. To ensure high performance of the entire WLAN, the 802.11b STAs will be disabled to access the network.

https://support.huawei.com/enterprise/en/doc/EDOC1000060368/7990aca/the-laptop-uses-the-80211b-g-nic-how-can-i-associate-it-with-a-80211n-ap