$ nix-build -A shrunk /nix/store/lv8zb0asgr222nfg02i2zm8xh0g6fwga-linux-5.4.84-shrunk
This is a subset of the module tree produced in the kernel derivation. The subset is specified by the
rootModules argument in stage-1.nix.
That subset is packaged as part of the initrd.
The lis of modules can be extracted with:
$ nix-instantiate --eval --strict -A root-modules