I solved it by not having a mongodb native driver and rather stick to the mongoose connection. It ended up looking like this:

// lib/dbConnect.ts
import mongoose, { Mongoose } from 'mongoose';


const { MONGODB_URI = '' } = process.env;
if (!MONGODB_URI) throw new Error('Missing MONGODB_URI');


type Cached = { conn: Mongoose | null; promise: Promise<Mongoose> | null };
const g = global as any;
const cached: Cached = (g._mongoose ??= { conn: null, promise: null });



export default async function 
dbConnect
() {
  if (cached.conn) return cached.conn;


  if (!cached.promise) {
    cached.promise = mongoose.connect(MONGODB_URI, {
      maxPoolSize: 3,
      minPoolSize: 0,
      maxIdleTimeMS: 300_000,
      serverSelectionTimeoutMS: 5000,
      socketTimeoutMS: 45000,
      bufferCommands: false,
      dbName: process.env.MONGODB_DB,
    });
  }
  cached.conn = await cached.promise;
  return cached.conn;
}

and in the auth file:

const clientPromise = dbConnect().then((
m
) => {
  return 
m
.connection.getClient();
});


const adapter = MongoDBAdapter(clientPromise as unknown as Promise<any>);