open source projects still need approvals for merging into a protected branch.

In other words, if you were to open source a project, others can view the code or submit edits to the code on a new branch. Just the mainteners of the repository (you and who ever else you choose to have that power) would need to check that new code and approve it.

If they made a change you don't want to implement, you just deny the change and no new code is merged.

That person could then (depending on licensing) make a fork of your project that does have their change implemented. This means they would make an entirely new project and they would have the ability to make changes.

You would still have full control on the original project that you created. And no changes would be pushed to an app store.

TLDR: if something is open source, it only ensures it's longevity and resilience. Open sourcing a project does not mean now that it is changed at the will of the internet without the express approval.