D&D (2024) Should shields, like Simple weapons be available to all characters?

[James Gasik]

and how long did it take to learn to brace correctly?

2 kicks? maybe 3?

learning to shoot a bow is hard, I have a longbow(or more precisely a recurve) and it takes time.

holding a plank of wood does not.

now, bashing with a shield and still managing to use it for protection, that takes practice, could that be a Fighting style or a Feat maybe?

I learned how to shoot a bow in an afternoon at the range. But I assume you mean shooting with any degree of accuracy.