TypeScript Error: FilterQuery with string _id not assignable to PipelineStage $match in Mongoose 9.1.5

[naveenkarmegam]

Description
When using FilterQuery<T> where T is an interface with _id: string (not ObjectId), passing this filter object to an aggregation pipeline's $match stage causes a TypeScript error in Mongoose 9.1.5.
The error suggests that RootFilterOperators expects _id to be compatible with ObjectId (or ApplyBasicQueryCasting<ObjectId>), but the interface explicitly defines it as string, causing an incompatibility even if _id is not present in the filter object.

Steps to Reproduce

1. Define an interface with _id: string.
2. Create a FilterQuery object for that interface.
3. specific the filter query to a $match stage in an aggregation pipeline.

Reproduction Script

import { FilterQuery, PipelineStage } from 'mongoose';

interface MyDoc {
  _id: string; // strict string, not ObjectId
  name: string;
}

const matchCriteria: FilterQuery<MyDoc> = {
  name: 'test'
};

// Error occurs here
const pipeline: PipelineStage[] = [
  {
    $match: matchCriteria
  }
];

Expected Behavior
The FilterQuery should be assignable to the $match stage input, as _id as a string is a valid use case (e.g. user-defined string IDs).

Error Output

Type '_QueryFilter<...>' is not assignable to type 'RootFilterOperators<{ [x: string]: any; _id?: ApplyBasicQueryCasting<ObjectId> | undefined; }>'
...
Types of property '_id' are incompatible.
  Type 'Condition<string | RegExp | string[] | null> | undefined' is not assignable to type 'Condition<((string | Types.ObjectId | ObjectId | ObjectId[] | undefined) & (string | Types.ObjectId | ObjectId | ObjectId[])) | null> | undefined'.

Versions

• Mongoose: 9.1.5
• TypeScript: 5.9.3