Forcing Stellarmate OS to Use 802.11ac WIFI ??

I'm running the Beta version of SM on a new RPi 4B, 4GB. So far it's working really well, connects to all my equipment perfectly and has been very stable. I'm testing the networking, trying to find the best/fastest connection possible. Obviously, the less extra gear I need and the fewer the cables, the better. I discovered that SM is only connecting with WIFI using wireless N at between 58 to 72Mbps. I have a wireless AC adapter on my laptop, and the RPi supports wireless AC, but refuses to connect using that protocol, only the slower N.

Is there a way to force SM to use 802.11ac for the fastest wireless networking?

FWIW, here are the three networking methods I've experimented with, all seem to work reliably while testing in my office:

1) Gigabit ethernet from SM to router, gigabit ethernet from router to laptop. 21MB images from my Canon T3i download in about 5 seconds.

2) Gigabit ehternet from SM to router, wireless AC from router to laptop (getting 433Mbps between router and laptop, downloading 21MB images takes about the same 5 seconds, maybe a fraction of a second slower.

3) Hotspot mode connecting completely wireless from SM to laptop, wireless N only (can't get SM to use 5Ghz AC) getting 58 to 72 Mbps, 21 MB images take about 10-11 seconds to download.

If you search this forum you will see that I had the same problem on RPI3b+ and changing the country code does not always work - e.g. Ubuntu Mate . Raspbian it worked. "Grey" imported AP's also seem to cause this problem as they are built for the country they are normally sold in and have different REGS/freq etc - its just a mess

Hope the country code works for you.

I already switched the country code to US, no luck. From what I'm reading, it's an opperating system issue - latest version of Raspian supports it. I thinking we may have to wait until a new release of Ubuntu Mate and hope it's been addressed.

Thanks for your reply Jasem!