从你粘贴的代码来看，你似乎没有导出subcat或category，而是导出了init函数。

const subcat = require("./subCategory"); // { initSubcatModel } and not a model

由于存在循环依赖，无论如何都会有一个问题，取决于init函数被调用的顺序，你会让subcat或category被undefined（因为相应的init函数还没有被调用）。
您应该将模型定义、模型关联和模型同步分成三个独立的步骤，确保首先调用模型定义，然后进行关联，最后进行同步。

// category.js
const { DataTypes } = require("sequelize");
const { getConnection } = require("../helper/databaseConnection");
const { getSubcatModel } = require("./subcat");

const categoryModel = {
  category_id: {
    primaryKey: true,
    type: DataTypes.UUID,
    defaultValue: DataTypes.UUIDV4,
  },
  category_name: {
    type: DataTypes.STRING,
    allowNull: false,
  },
};

let category = null;
const getCategoryModel = () => {
  try {
    if (category) return category;
    const sequelize = await getConnection();
    category = sequelize.define("category", categoryModel, {
      freezeTableName: true,
    });

    return category;
  } catch (err) {
    console.log("category", err);
  }
};
const associateCategoryModel = () => {
  const category = getCategoryModel();
  const subcat = getSubcatModel();
  category.hasMany(subcat, {
    foreignKey: "category_id",
    onDelete: "CASCADE",
  });
}

module.exports = { getCategoryModel, associateCategoryModel };

// subcategory.js
const { DataTypes } = require("sequelize");
const { getConnection } = require("../helper/databaseConnection");
const { getCategoryModel } = require("./category");

const subcatModel = {
  subcat_id: {
    primaryKey: true,
    type: DataTypes.UUID,
    defaultValue: DataTypes.UUIDV4,
  },
  subcat_name: {
    type: DataTypes.STRING,
    allowNull: false,
  },
};

let subcat = null;
const getSubcatModel = () => {
  try {
    if (subcat) return subcat;
    const sequelize = await getConnection();
    subcat = sequelize.define("sub_category", subcatModel, {
      freezeTableName: true,
    });

    return subcat;
  } catch (err) {
    console.log("sub category", err);
  }
};

const associateSubcatModel = () => {
  const subcat = getSubcatModel();
  const category = getCategoryModel();
  subcat.belongsTo(category, {
    foreignKey: "category_id",
    onDelete: "CASCADE",
  });
}

module.exports = { getSubcatModel, associateSubcatModel };

// index.js

const initModels = async () => {
  const category = getCategoryModel();
  const subcat = getSubcatModel();

  associateCategoryModel();
  associateSubcatModel();

  await category.sync();
  await subcat.sync();
}