@Jan-Erik, Software is opinionated when it is rigid to a certain way of thinking.
Think about Apple and their walled garden. You can’t do much there unless Apple allowed it explicitly. Apple has opinions on how things should work and their phones reflect those opinions by locking you down so you can operate only in the ways they want. It’s not flexible, but it works well if you don’t step outside the limits.
In contrast, Android is far more flexible and adaptable to many situations. It has far fewer opinions on the “right way”, and what you see is far more adoption in many markets because it places less limits on various use-cases. It is also is a bit of a mess and with far less coherency across devices or vendors. You gain flexibility, but lose the benefits that come with a vision laid down by an singular architect.
RoonServer is super flexible and you can run it on Mac/Windows/any-Linux-Distribution. It lacks strong opinions on the environment it runs in. On the other hand, RoonOS is highly opinionated on the “right way” and isn’t flexible at all.
With flexibility comes complexity, maintenance, and environments prone to errors. Roon OS was built to eliminate that, but it comes with strong opinions on what’s the right way to accomplish the “goal”.
I hope that was clear.