I use this wifi settings for a pre-installed SD card: Can I add WiFi config to SD card pre-install? (headless setup)
This works fine. Can I force with this method also a connection via 5Ghz?
The SSID from 2,4Ghz and 5Ghz are equal. I can't change it.
I use an external wifi adapter: Edimax EW-7811UTC. It works with 5Ghz, but it is often changeing between 2,4Ghz and 5 Ghz.