@rickyzhang
My Studio is normally wired but I just did a test and it runs on WiFi6 only at the limit of my connection speed (1GB).
I'm wondering if there's some nearby interference on your 802.11ax channel.
Before you trudge off to the "Genius" at the Apple store have you tried moving the Studio to a different location in your workspace? Have you tried a different channel for 802.11ax?