Mac Mini M4 WiFi Issue

I purchased a new M4 Mac Mini running Sequoia about a 3 weeks ago. I have a solid WiFi mesh system providing about 350mbps up and down (my smart phone gets 230mbps when I am sitting beside my Mac). I have begun to notice that my WiFi on the Mac can run very slowly - down to circa 35mbps. I thought I had solved the issue by moving my Western Digital external hard drive 3 ft away. But the wifi appears very inconsistent even with the extenal drive some way away - sometimes at 25mbps then up to 200mbps.

Is there a shielding issue with the mini? I cannot run it off ethernet and I need to have a solid reasonably reliable wifi system. This is NOT a WiFi problem since other devices in the house are fine.