I mean like this (simplified with 1p):
System A is cinfigured as a normal offgrid system with PV
System B has a ESS config with energy meter between A and B
In this config, you can even switch off system A if no loads are present, system B is unable to handle them, or battery B is empty or full. This will safe some Power.
With the bypass switch you can use system A, when B is down.
Behind this are the loads and PV