I think the obvious answer right now is anything related to AI. But I'm actually quite excited about the embrace of open-source applications that traditionally have not been, such as Cal.com and Mattermost.
I agree that open source, or even more specifically open and interoperable protocols between applications/sandboxes is where the next leg of software growth will happen on the internet. I don't believe increasing centralization is a trend but rather a swing of a pendulum that would start inverting soon. It will be less about open equivalents of centralized/closed products and services but just the birth of something new with openness and interoperability at the core.
Open source is trending up again these days. Lots of companies (like the ones you pointed out) are trying to be the cloud hosted offering of something that's open source. Love to see it!