I think you should try a few different things out before you judge all software engineering jobs. There's a big variety.

As for "making shitty bloated proprietary software" that only really applies to the really big tech companies and banks etc.. Most dev jobs are about using code to solve a problem. I've worked in lots of small companies and we use open source software almost exclusively. If there's anything you write that you think could be useful as an open source project, they'll generally let you spin it out into a standalone library and you can spend some of your working time on that. The company benefits from increased visibility and can be a "thought leader" at conferences etc if it takes off. Definitely worth asking about that in the interview though, since different companies will have different philosophies around it.