I got a new MBP a couple of weeks ago and I’ve been migrating things to it from my previous 2015 MBP. A couple of days ago I went to a different site on my UniFi network, and unexpectedly WiFi performance on the new MBP M2 was abysmal (as in 0.5 Mbps down). On the old MBP I got the full uplink speed (which is 4G, and getting about 36 Mbps on a Friday night is “great”).
Eventually I found an Ubiquiti forum post that provided the solution: change the 5 GHz radio channel. The post pointed at DFS channels being the problem, but I’ve already avoided using them where possible. So in my case I switched from channel 36 to channel 44. This improved the WiFi speed on the MBP M2 to 150 Mbps down. I must note that on the 2015 MBP I was also getting just over 100 Mbps down, so the 4G must have been much less crowded as well (early on a Saturday morning).
When researching the issue I saw it is not an uncommon issue to have. Some other sources suggested that turning off Bluetooth would help, but it didn’t for me. I’m also glad that I didn’t need to turn Bluetooth off, as that is how my headset is connected.