Congratulations on leaving Microsoft. Unless you have bills to pay, you won’t regret it. I left at the end of 2004, and have since studied a vast and amazing — but still flawed – world of computing out there.
For example, I discovered that we should already have cars that (optionally) drive us around and computers that talk to us. And that Linux on the desktop is powerful and rich but failing because of several strategic mistakes. Google claims to be a friend of Linux and free software, but most of their interesting AI code is locked up. Programming should be a part of basic math literacy for every child. The biotechnology world is proprietary like Microsoft, which is stunting progress in new medicines and safer devices.
The most important lesson is that the free software world outside Microsoft is much bigger and richer. No matter what aspect of technology you want to work on, there are codebases and communities out there. Even the large companies who write proprietary software like Amazon, Apple, Facebook, and Twitter use free software as their base. So you first find out what you want to work on, and then you find the existing codebases and communities to join. In some cases, the are multiple, so you need to decide which best meets your needs.