I meant to ask if they can be purchased while traveling or do they have to be purchased in the US where I will be traveling from?

You’re mixing up some terminology. As a non-European citizen you can only choose for a Eurail pass.

Each pass comes in two variants: a one country pass (to use in one country only) or a global pass (to use all over Europe), and then it differs in terms of continuous usage (like a month of continuous travels) or a flexible usage (to use on x amount of travel days, during 1 or 2 months).

This is a good guide: https://www.seat61.com/how-to-use-a-eurail-pass.htm

Doesn’t matter where you buy them. As a non-European citizen, you need a Eurail pass, not an interrail. It’s linked to country of residence, not where you buy it :)

Perfectly fine to buy them on the road during your travels.

Thank you, @BrendanDB. I have traveled in Europe before and got the pass for like 15 days. I wasn’t sure if the pass would work the same if I want to use it to travel between Scotland, Ireland, and London. Can you answer that?

Well, Eurail is a RAIL pass, between those places there is quite a lot of water so ferries or planes required. There are small discounts on some of the ferries with a Eurail pass.

Scotland and Ireland are also less well served by rail than many places, particularly some of the more scenic remote areas and some notable tourist locations.

 I think that what you ought to do is work out where you want to go, do and see and then find the best travel options for those rather than commit to a specific ticket first.

It really depends on what interests you.