Are you having problems getting null and steam to connect? Or problems with your game starting with both steam and null online subsystem? This project defaults to steam if steam is running, then falls back to null if it is not.
Steam clients and null dedicated servers used to work great until 4.19? or so. Now mixed online subsystems won’t be allowed to connect due to a check when a client connects. I think Epic might correct the issue in the next release. I haven’t tried 4.22 yet but they are aware some people complained about the mixed subsystem check.
We are waiting to see what the new subsystem will be like before changing too much. Hopefully Epic addresses some issues.
If that doesn’t answer your question, let me know what specifically you were wondering?