using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Conventions;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.EntityFrameworkCore.Extensions;
using MongoDB.EntityFrameworkCore.Metadata.Conventions;

var client = new MongoClient("mongodb://localhost:27017");

using var db = CustomerDbContext.Create(client.GetDatabase("test"));

var sally = db.Customers.First(x => x.FirstName == "Sally");
Console.WriteLine(sally);

class Customer
{
    public ObjectId Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int FavouriteNumber { get; set; }
    public override string ToString() => $"{FirstName} {LastName} ({Id}) - {FavouriteNumber}";
}

class CustomerDbContext : DbContext
{
    public DbSet<Customer> Customers { get; init; }

    public static CustomerDbContext Create(IMongoDatabase database)
    {
        return new CustomerDbContext(new DbContextOptionsBuilder<CustomerDbContext>()
            .UseMongoDB(database.Client, database.DatabaseNamespace.DatabaseName)
            .Options);
    }

    public CustomerDbContext(DbContextOptions options) : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        var customerModelBuilder = modelBuilder.Entity<Customer>();
        customerModelBuilder.ToCollection("customers");
    }
}

use test
db.customers.insertOne({
    FirstName: 'Sally',
    LastName: 'Smith',
    favourite_number: 42
  })