It may take some playing around to get the right chain length. You want the chain long enough to be able to just about shift into big-big. Not that you’d ride cross chained like this, but in the event you inadvertently shift into big-big, you don’t want to rip the chain/derailleur off the bike.
In small-small, you want the chain to be short enough to have some tension left in it so it won’t easily drop.
There’s probably only one chain length that will allow you to do both.
I have 50-34, and 11-40 set up this way with a roadlink and medium cage ultegra derailleur. I did this to convert my road bike into a gravel bike. Worked great.