Mac Mini M4 wifi problems

1) The Mac mini's wireless antenna is built into the bottom cover.

2) The wireless chip and antenna are in close proximity to the high speed Thunderbolt/USB ports.

Have a look at > Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

1) Make sure that there are no solid metal walls, objects, or appliances in-between the Mac mini and router.

2) Make sure that there are no poorly shielded high speed USB cables, drives, devices near or in-between the Mac Mini and router.

Sometimes the best solution, is to stand the Mac mini on its side with the bottom facing in the direction of the router.

What modem/router (make and model) do you have?

Are you able to connect the MBA to your router via Ethernet? If you can see what speed you can get that way.

Have you checked with your provider to see if the installation is OK. What were their recommendations?

Try the following:

1 - Shut down your MBA, iPad, router and modem (if they are separate).

2 - restart the devices in this order: modem, router, MBA and iPad.

Check to see if there's any improvement.

I have an M4 Mac Mini Pro and if you press the option key and the network icon in the menu bar you will see the connection speed to your router change constantly. Did that on my M1 Mac Mini, and also on my M1 MacBook Pro. This may be a function of Apple's Broadcom chip selection and behavior.

Even eliminating the router by providing a Wi-Fi 6e signal from my NetGear NightHawk M6 Pro (MR6550) hotspot, the M4 mini Pro still varies the connection speed though not as widely as it does with Wi-Fi 6 from my Synology RT6600ax router.

My M4 Mac Mini Pro is sitting on its side (closest to the power light) for easy access to the power button, but also in hopes of minimizing the Wi-Fi speed variance by facing the router that is 20 feet away.