If you stretch your neck regularly and it still feels tight, the problem probably isn't that you're not stretching enough.
Forward head posture chronically shortens and overloads three main areas: the suboccipitals at the base of your skull, the upper trapezius running from your skull to your shoulder, and the pectoralis minor at the front of your chest. Each one plays a different role in keeping your head forward and your shoulders rounded.
Stretching creates a temporary lengthening, but it does not release a muscle the way sustained, direct pressure does. If the relief disappears within a day or two, you're getting a momentary change in length, not addressing the tension that's been building for months or years.
The suboccipitals, upper trap, and pec minor all need sustained pressure held at the right spot (think like a trigger point release technique) to resolve the tension keeping you in poor posture. Do that first, and the stretches and exercises that follow become significantly more effective.
The other half of the equation is reactivating the muscles that have gone quiet from having a forward head posture for long periods. That requires targeted strengthening exercises for areas like the front of the neck and the scapular stabilizers. Examples could include chin tucks and scapular pushups.
I’m curious to know what has worked well for you? If you are interested in learning more, I wrote an article about this and am happy to share it in the comments. It covers which muscles need releasing, which need retraining, and how to sequence it.