Netgear A6210 to Slow

i am using the Netgear A6210 on my LINKSYS1900ACS OpenWrt 19.07.3 r11063-85e04e9f46 .

I use the Netgear USB WIFI stick to connect to my Internet Providers Router over 5GHZ and i am using this interface as WAN for my LINKSYS WIFI

So if i connect now to my WIFI on the Linksys i only get maximum 120MB/s if i connect a network cabel from my Internet Provider to the Linksys i get 250MB/s over the Linksys WIFI

I used the Driver for Netgear kmod-mt76x2u. So i tried to connect from my Notebook to the Internet Provider Wifi witch the Netgear is connection and i got 250 Mbit/s so i guess it is a issue from the Netgear A6210 maybe the driver?

Can annyone help me with this please? Why i got the Limitation?

because Linksys wireless interface is STA and AP mode at the same time? i.e. it's connected to a wireless access point (netgear a6210) while creating it's own wireless network (linksys wireless)

This divides the usable wireless bandwidth.

I dont get this one the Linksys has his own AP on 5GHZ and the Netgear A6210 is connected to my Internet Router over 5Ghz and acts like a WAN.

I mean both are different Hardware right?

Yes, but Linksys 5ghz wireless is connected to the a6210 and to your client at the same time. i.e. 5ghz band is being used as STA and AP at the same time.

Do you mind sharing a screenshot of luci>wireless>ac-band.

Two radios physically next to each other on the same band tend to jam each other, even on different channels. It may work better to use the same radio as both the AP and STA because the operation will be synchronized.