Install M2 NVMe drive with WiFi A+E key adapter

I have the below J6412 soft router. I want to install a second M.2 NVMe drive in the M.2 WiFi slot using an adapter.

My question is: what size NVMe drive will fit in this second slot? Can I fit a full-size 2280 drive, or do I need to use a smaller one (2242 or even 2230)?

If it will not fit a 2280 drive by default, is there any custom mounting or external adapter that I can use?