Do I need to state private fields when declaring a class?

I am getting the following error:

Argument of type '(obj1: Class1) => JSX.Element' is not assignable to parameter of type '(value: Class1, index: number, array: Class1[]) => Element'.
  Types of parameters 'obj1' and 'value' are incompatible.
    Type 'Class1' is missing the following properties from type 'Class1': _privateField1, _privateField2 ts(2345)

I declare Class1 with the following code in ./global/types.d.ts

declare type ClassA = import('third-party-library').ClassA;


class Class1 extends ClassA {
  // Inherited properties
  inheritedProperty1: number;
  inheritedProperty2: number;

  entity: Entity | null;
  readonly id: string;

  constructor(superProp1, superProp2, obj1: Obj1Type);
}

which is defined here in ./model/Class1.ts:

class Class1 extends ClassA {
  private _entity: Entity | null = null;
  private _id: string;

  get id() {
    return this._id;
  }

  get entity() {
    return this._entity;
  }

  set entity(entity: Entity | null) {
    this._entity = entity;
  }

  constructor(superProp1, superProp2, obj1: Obj1Type) {
    super(superProp1, superProp2);

    this._id = generateId();
  }
}

export default CustomHex;

tsconfig.json:

{
  "extends": "expo/tsconfig.base",
  "compilerOptions": {
    "strict": true,
  },
  "include": ["**/*.d.ts", "**/*.d.tsx", "**/*.ts", "**/*.tsx"]
}

Why do private fields need to be declared with the class? Is there a better or another way to organize my project besides adding private fields to ./global/types.d.ts?

The reason I am not importing type Class1 from ./model/Class1.ts is because Class2 or others may use Class1 (and vice versa) which would create a circular dependency.