The best of these kinds of teams work together over longer time, and on problems they can feel ownership on. That's where my life gets complicated.
The wonderful little team I work with, works in an organization that works with the ideals of internal open source project. The team has no nice list of microservices they'd be responsible for, but anything and everything anyone has ever created into the overall system is up for grabs.
As a tester in a team like this, I find it fascinating to look at how people approach the problem of modeling their responsibilities differently.
One tester seems to model their actions on the team's developers actions. If a developer goes and changes something, a tester follows and helps tests the change. A lot of this activity happens by the developer pulling someone other than themselves to implement automation.
One tester seems to model their actions on the end to end flows of the system, from the perspective of mention-worthy functionalities being introduced. None of this activity happens by the developer pulling people in, but the tester pushing ideas of seeing value in the system perspective.
One tester seems to model their actions on collecting any work anyone would wish a tester would do. Whatever needs doing and looks like being dropped by others ends up as things they do.
Explaining and understanding where the time goes and what activities belong with "a team" can get very complicated. I guess it also makes sense that its also a high trust environment, where doing is considered more relevant.