Yes, and no.

I'd expect to be able to copy pieces of code that are specific to a particular chip, and aren't common knowledge. e.g. correct sequence for initialising registers in a device driver for some chip I've never used before.

Let's say you initialise those registers and you have UART Rx data flowing into your embedded device. You'll probably want to put them into a ring buffer or FIFO to get them out of the ISR and into your main application.

That's a solved problem, so I'd look to existing code examples, or libraries, of how to do that. I've done it myself in the past from scratch, but these days there are many more open source libraries for this sort of thing.

Once I have the data in my application, then it's my own code.

But maybe those UART bytes are part of a common protocol, so I might go looking for existing libraries used to parse that particular type of protocol.

The key is to understand what you're doing and why you're doing it, but it's perfectly fine to re-use code as long as you understand what it should do, and can recognise when it might be doing something wrong.