Does the AW7916-NPD card work stably in AP mode?

Does the AW7916-NPD card work normally as an AP in your case?
I just installed OpenWrt on x64 machine, hostapd and firmware for the AW7916-NPD card. 2.4 GHz band works normally, but the 5 GHz band it works terribly... I set the channel to 100 and after many interface restarts and configuration changes, the SSID is visible to WiFi devices, then the transfers are fast. But then it turns off and doesn't get up again. This is a nightmare... Currently, I have one preferred channel set to 100. How can I set it to be active immediately and not disconnect?

If I'm not mistaken this is a DFS (radar detection) channel in several regulatory domains. Depending on where you are and what regdomain (country code) your adapter is set to (hopefully those match), it might not be the adapter itself but rather hostapd or actual signals being interpreted as radar and no alternate channel set in your radio configuration. Maybe try another channel and/or alternate channels (see channels in the reference doc).

Thank you, I switched from 2.4GHz to 5GHz AP.I just realized that channel management is a very complicated issue in the 5G band.
And the fact that a given card does not work as I expected (and what I was used to) is rather a matter of restrictions imposed by regulators.

Yeah there's more regulation involved at 5GHz but that doesn't mean you can't use it. It just takes more configuration and trial/error. Maybe start with channel 36 as it tends to be less complicated regulation-wise. Of course it depends on how busy it is with other APs in your location. I use the open source WiFiAnalyzer app on android to scan my WiFi "environment".