I don't have any clues of how I can connect my micro:bit to Srcath without using Bluetooth as my PC didn't come with a Bluetooth adaptor. Sure, I can buy one but in the meantime what can I do?

(I would like it if you can do it a way with Vanilla Srcath)

You can't really, unless you were to make your micro:bit appear as a keyboard over USB, but doing that would require some knowledge of a low-level language (such as C or C++, or possibly Python) and how to compile it to a .hex file. Still, you might find some insight at the micro:bit developer site: https://tech.microbit.org/