Hard to breathe during meditation I started with a new goal: meditate for a month daily and it reminds me of my experiences during group meditations in the past. After relaxing the body, it gets very hard to breathe, my chest feels very heavy or like something is on top with a lot of pressure. I feel like I should breath deeply all the time, yet still feel like I don't have enough air. A bit scary too. Has anybody experienced the same?
it's not enough air. A bit scary too.

It's quite difficult to give detailed advice over the internet. What you describe is actually somewhat concerning. The best advice would be to seek out someone who could watch your meditation and advise.

For example, a common reaction to fear can be to hold one's breath so that a predator cannot detect our breathing. Meditation should feel relaxed and secure and peaceful, especially if you are alone without support. Simple things like poor posture can magnify suppressed anxiety. For example, if my chin is sticking out a bit, then fear tends to arise. However, if I am sitting straight and relaxed, chin in and back of neck smooth and unkinked, then I feel secure and fear evaporates.

Please do seek at least a friend who can compare your sitting posture with a picture of a meditating teacher. Such a friend would be a good spiritual companion.