//test code
var client = new MongoClient(_host);
var db = client.GetDatabase("healthcare-db");
var dbContext = MongoDbContext.Create(db);
var item = new SampleObject()
{
    Name = "test",
    Age = 10,
    Weight = 100
};
await dbContext.Samples.AddAsync(item);
await dbContext.SaveChangesAsync();

// here error "The source argument must be a MongoDB IQueryable"
var items = await dbContext.Samples.AsQueryable().Where(m => m.Name == item.Name).ToListAsync();

//...

//dbcontext
public class MongoDbContext : DbContext
{
    /// <summary>
    /// ctor
    /// </summary>
    /// <param name="options"></param>
    public MongoDbContext(DbContextOptions options)
        : base(options)
    {
    }
    
    public static MongoDbContext Create(IMongoDatabase database) =>
        new(new DbContextOptionsBuilder<MongoDbContext>()
            .UseMongoDB(database.Client, database.DatabaseNamespace.DatabaseName)
            .Options);

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
#if DEBUG
        optionsBuilder.EnableSensitiveDataLogging()
            .EnableThreadSafetyChecks()
            .EnableDetailedErrors();
#endif
        
        base.OnConfiguring(optionsBuilder);
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {   
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<SampleObject>().ToCollection("samples");
    }

    public DbSet<SampleObject> Samples { get; set; }
}


public class SampleObject
{
    [BsonId] 
    [BsonElement("_id")]
    public ObjectId _id { get; set; }
    
    [BsonElement("name")]
    public string Name { get; set; }
    
    [BsonElement("age")]
    public int Age { get; set; }
    
    [BsonElement("weight")]
    public double Weight { get; set; }
}