MacBook Air M2 loosing WLAN 5GHz connectivity

It's more likely an issue with your environment (network neighborhood) or router settings than with the MBAir hardware. Also, keep in mind that 5GHz WiFi connections will almost always be weaker than 2.4GHz.

Experiment.

• Set your router's 5GHz network to a specific 20Mhz channel. For purposes of testing it may be best to use channel 165 or 169 (assuming no contention on those channels in your environment).
• If the 20 MHz connection works fine, reset your router to one of the 40MHz channels (e.g. 159 or 167) and try again.
• If the 40 MHz connection works fine, reset your router to one of the 80Mhz channels (e.g. 155 or 171).
• And if 80MHz works fine, try 160Mhz (e.g. channel 163)
• Without knowing your specific router, you may also need to verify that the correct bandwidth is being used for the channel you select each time.
• Reboot your router *and* your MBAir for each trial run.
• Make sure your MBAir is in the same room as the router with nothing blocking the view between them.
• At some point in this process you should discover what works and what doesn't.

For more information, see:

Wi-Fi and Ethernet specifications for Apple devices - Apple Support

How Apple devices join Wi-Fi networks - Apple Support

Not sure I can be of any more help here.

Except to say that I do not recommend using *any* DFS channel. DFS channels share spectrum with Weather and Radar systems. When a WiFi device detects a weather or radar signal it must stop using the DFS channel, switch the channel if possible, or even stop transmitting for 30 minutes ... but if your router is set up to use a fixed channel, neither the router nor your client devices can switch.

If you must use a fixed 5GHz channel, stick with 36, 40, 44, 48, 149, 153, 157, or 161 (20 MHz) or one of the 40Mhz or 80MHz channels associated with those channels. These are the non-DFS channels.

Also, in my experience late-model (M-series) Macs are considerably more sensitive to WiFi signals than their predecessors. For example, my M4 MBPro detects many more channels in use in the neighborhood than any of my older Intel-based Macs do. At first I was puzzled by this but it turns out the radios in newer Macs are much improved and more sensitive. It's "possible" that your MBAir M2 is detecting DFS signals that your other devices don't.

ps. If you want to check for network contention, use Network Diagnostics.

• Option-click the WiFi icon in the menu bar
• Select Open Wireless Diagnostics
• Do not click the Continue button
• In the Wireless Diagnostics menu strip (top left of screen), click Window > Scan > Scan Now

This will give you a report about all the WiFi networks in your environment and, among other things, you can see where there is channel contention (congestion).

If you are interested in seeing a visual map of the channel environment, and more diagnostics, WiFi Explorer is a good app. It's available from the developer or from the App Store.

Check the connection type on each Mac & iPhone to see if there is any difference in your MBAir ... what channel, speed & bandwidth is each showing in use? Are there any differences?

According to the specs,

• The MBAir supports WiFi 6 (802.11ax)
• The older Intel MacBooks support WiFi 5 (802.11ac)
• Don't know your iPhone models, so I can't say there
• What does your router support?

Are you using any VPN or security (a/v) software on your MBAir?