Here is a MWE:

{
  pkgs ? import <nixpkgs> { },
  lib ? pkgs.lib,
}:

let
  testSubmodule =
    { config, ... }:
    {
      freeformType = lib.types.lazyAttrsOf lib.types.raw;

      options.a = lib.mkOption {
        type = lib.types.int;
        default = 0;
      };
    };

  isSubmoduleFn =
    m:
    let
      args = builtins.functionArgs m;
    in
    args ? lib || args ? config || args ? options;

  staticInnerType =
    let
      baseType = lib.types.addCheck (lib.types.submodule testSubmodule) (
        v: builtins.isAttrs v || isSubmoduleFn v
      );
    in
    baseType
    // rec {
      functor = baseType.functor // {
        type =
          attrs:
          let
            mergedType = lib.types.addCheck (lib.types.submoduleWith attrs) (
              v: builtins.isAttrs v || isSubmoduleFn v
            );
          in
          mergedType
          // {
            inherit substSubModules;
            functor = mergedType.functor // {
              inherit (functor) type;
            };
          };
      };

      substSubModules =
        m:
        lib.types.addCheck (lib.types.submodule m) (v: builtins.isAttrs v || isSubmoduleFn v)
        // {
          inherit substSubModules;
        };
    };

  dynamicInnerType = lib.types.functionTo staticInnerType;

  innerType = lib.types.either staticInnerType dynamicInnerType // rec {
    substSubModules =
      m:
      (lib.types.either (staticInnerType.substSubModules m) (dynamicInnerType.substSubModules m))
      // {
        inherit substSubModules;
      };
  };

  testType = lib.types.lazyAttrsOf innerType;

  optionModule1 = {
    options.test = lib.mkOption {
      type = testType;
    };
  };

  optionModule2 = {
    options.test = lib.mkOption {
      type = testType.substSubModules [
        {
          options.b = lib.mkOption {
            type = lib.types.bool;
          };
        }
      ];
    };
  };

  staticConfig = {
    config.test.random2 = {
      b = false;
    };
  };

  dynamicConfig = {
    config.test.random1 =
      { arg1 }:
      {
        a = 1;
      };
  };

  result = lib.evalModules {
    modules = [
      optionModule1
      optionModule2

      staticConfig
      dynamicConfig
    ];
  };
in
result