See reply #2: You need a magnetometer for stable yaw values. The MPU6050 does not have one.

The MPU6050 library developers understand this simple point.

Maybe different wording will help @dsyleixa with his lack of understanding of the situation:

When an IMU is perfectly still, the pitch and roll can be calculated precisely because gravity provides a point of reference for the Z axis. The gyroscope is imperfect and will drift. If you rely 100% on the gyroscope for pitch/roll, it will soon have nonsense values (especially with $0.45 parts like the MPU-6050).

To get an accurate yaw angle, you need a point of reference which is 90 degrees rotated from gravity. The magnetic poles do a good job of this. Without a point of reference, you have NO WAY OF EVER CALCULATING an accurate yaw angle. If you start from a known position and just use Z axis rotation of the gyroscope to calculate the yaw angle, you'll quickly have a value that is wrong.

You keep claiming to know nothing about Kalman filters, raw values, libraries, etc. It would help you to understand if you took the time to learn how an accelerometer + gyroscope work so that you can understand the information provided and its limitations.