It has to be 3020MT.

this 5.7 inches video card will fit physically.  its TDP is 65 w.

AMD Radeon R5 340X OEM Specs | TechPowerUp GPU Database

well according to dell support it shows that it will be able to work  says the link 

https://www.dell.com/support/home/en-hr/drivers/driversdetails?driverid=kdgmg#:~:text=This%20package%20contains%20the%20AMD,64%2Dbit)%20operating%20systems

you are correct.  there is low profile R5 340X that may work in 3020 SFF.