Are all computers capable of having Fiber Optic internet? If not, how do I know if my computer is?

Fiber Optic is merely a different way to deliver internet to your home. You can get internet through satellite or a cable company or like I do from a tower broadcasting a WIFi signal. You can also get internet through 5G or cell phone frequency. Remember when we used to get our internet through the phone with all it beeping and buzzing! Fiber optic is probably the best quality internet you can get. I'd kill for it out here in the country! They lay the fiber optic cables along the street and then run the connections to your house. Your computer doesn't care WHERE you get your internet is the good news!

So, my computer doesn't need any special part for me to get Fiber internet? That's what I want to know. As far as I know, I'm only good to go with an Ethernet connection. I don't know how fiber works.

I second Draclvr here. The computer doesn't care and won't need any new parts. On the other hand the fiber needs to be connected to some new little box somewhere in your house. Then typically you just plug in your ethernet cable in that box. A bit like the old phone modems but without the beeping and buzzing. Those boxes usually also offer WiFi connection as an extra option but that's not necessary to use.