Also, I tried to use my bluetooth headphones with my Macbook air, even knowing the steps, and it said I had to upgrade the OS to use them (I think the OS was like a year old at the time, and the computer four years old -- El Capitan, I think?)

Seriously? Both OSes knew the version of the bluetooth protocol they needed to use to communicate, and it still doesn't work? Never had that problem with a headphone jack.