Dell optiplex 9020 ALL IN ONE eGPU

I think 9020 AIO uses miniPCIe wifi cards such as 

here are DP/N for them

so it does not have the newer M.2 slot for WiFi card.  I am not sure if you can install a GPU in the onboard miniPCIe slot (white slot 13285P shown on your pic).

Mini-PCIe GPU adapters do exist, but note:

1.  The bandwidth of the slot is a tiny fraction of what a GPU needs -- so you won't get anywhere near the expected graphics performance, if the adapter even works,

2.  You can't backfeed the video into the screen, so you'll need to feed the output to an external monitor.

3.  You won't be able to close the case of the all in one with the cables required to connect to the external GPU box.

If you need a desktop with a better GPU, buy one -- the limitations of attaching a GPU to a wireless card slot will diminish greatly the return on what you'll spend.  A true desktop system will run a GPU at full speed -- and even a decent used desktop system will likely not cost much more than just an external GPU box and power supply.