iPad Air2: wifi does not work normally under IOS13

Here is a support page that documents Apple recommended WiFi setup:

Recommended settings for Wi-Fi routers and access points – Apple Support

Whilst WiFi has a set of standards, not all manufacturers of WiFi infrastructure devices (WiFi Routers and Access Points) fully or correctly implement the standards. Wider channel bandwidth settings are often an area where issues will occur - and contrary to popular misconception, often do not improve network performance.

Wider channels result in fewer non-interfering channels - which can be an issue for both your own and neighbouring WiFi networks. Higher throughput performance - and improved range/penetration - can often be realised by using more concurrent streams of lower channel bandwidth.

As your internet connection is the limiting factor for throughput, unless you are attempting high volume data transfer between devices on your local WiFi network, high headline throughput figures for your WiFi is pointless. Consider also that WiFi is a contended connection - that reduces practical throughput where multiple client devices connect to the same WiFi network segment (SSID).

Yes, I’m fully conversant with WiFi standards - and equally have optimised many such systems.

My own home-office network utilises three separate network segments (SSIDs), two supporting 802.11ac, one of which is also dual-band for flexibility. For reasons beyond this scope of this discussion, multiple client types are fully supported with excellent stability and throughput; none are using 80MHz (or greater) channels. I am misfortunate in having having a considerable number of neighbouring mixed-mode 5GHz and 2.4GHz networks - and have been successful in maximising performance in a channel constrained environment.

As an engineer, you should appreciate that network optimisation needs to allow for the lowest common denominator - in this case, the oldest device in your device inventory that you wish to fully accommodate on your network.

Technology moves on. Whilst we can maintain backward compatibility with older devices, we often have make a choice. Either we must find a configuration compromise that provides adequate/optimised performance for the full estate - or we eliminate support and retire older hardware. iPad Air2 is still in support - but its WiFi hardware may not be cutting-edge.

Your remainIng options are to contact Apple Support (you’ll find the Contact Support link at top-right of this page) - or you can post feedback to Apple using the appropriate product feedback page:

https://www.apple.com/feedback/

Whilst I am evidently unable to provide advice and guidance that meets you requirement to utilise “wide channels”, I wish you well in finding an acceptable solution to your problem.

You correctly observe that 40/80MHz channels are supported - but are not necessarily recommended or offer best overall performance for your environment.

Have you ever come across the concept of Network Optimisation...? Turning-up all settings “to max” doesn’t necessarily produce the best (or an acceptable) result. The trick is to find the best performing settings for your devices and the environment in which it operates.

Consider also that you are likely to be using a WiFi Router/AP that might not be particularly “friendly” with your iPad. Different manufacturers hardware can have significant impact upon compatibility and overall perfomance.

Sorry, but this is the very best overall advice that I can offer. I sincerely hope that you find it to be helpful in producing the best performance for your set of circumstances.

Postscript Edit: I wouldn’t get too hung-up over WPA3. A Security vulnerability has been identified; until effectively patched, WPA2 remains more secure.