symbol supports to run a hierarchical (call a .qsch) or a sub-circuit (call a .subckt).
If you convert your hierarchical structure into a subckt, you can create a symbol with embed .subckt included, which means, simulation can run with only a .qsym file.
This is a post from Mike Engelhardt for your reference
Best Directory structure and library path definitions for Hierarchical schematics and reusable symbols - QSPICE - Qorvo Tech Forum
I have a reference guide ( Qspice - General Reference Guide by KSKelvin.pdf ) which discuss about this in Part 2.
Or, you attach your gain.qsym and gain.qsch, and I show you the step in converting this hierarchical into a subckt symbol.