Hi,
After installing the snapshot of June 22nd, wpad (full version) and the kernel modules for the usb wifi (kmod-mt7925-common, kmod-mt7925-firmware, kmod-mt7925e, kmod-mt7925u, mt7925bt-firmware) I set to encryption to WPA2. I couldn't WPA3 to work.
I like to have 2.4GHz (for older clients) and 5GHz. So I bought the USB wifi.
Connecting to the Pi5 on board wifi (set to 2.4GHz) is fine.
Connecting to the USB wifi device causes the Pi5 to reboot.
Any way to solve this?
Powered USB hub?
Proper router as AP instead?
Powered USB hub?
No. USB wifi is connected to the Pi5
The Pi5 is the router. It is connected to a Waveshare 4 Port ethernet board.
You asked how to solve the issue, suggestion was given.
Router/AP will most likely cost as much as the powered hub.
The point @frollic was making is that you probably need to use a powered hub. One likely issue is that the Pi cannot provide sufficient power to the wifi usb dongle and system is browning out.
The Pi4 and Pi5 devices make fine wired routers, but for wifi, you should really use a proper purpose-built AP (these include all-in-one wifi routers) since they are actually designed for wifi. The Pi's built-in wifi is extremely low end and low performance, and USB dongles aren't much better especially since most of them are designed first for STA use (not AP) and they can cause problems like what you're seeing.
@psherman Thanks for the explanation.
I know the Pi5 isn't the greatest device for this but I wanted to try it.
I'll have to decide to buy a powered hub just to see if this solves it or just replace my old AP with a new purpose-built one.
When I go for the latter I have a spare Pi5 
Your old AP (used as an AP only) will probably outperform the wifi dongle you're trying to use now. You can continue to use the Pi as a wired router, of course, but I'd recommend cutting your losses and working with a proper external AP instead of buying a powered hub to enable the use of what is likely to be a relatively poor performance option (usb wifi dongle) anyway.