It's infuriating. Nothing else behaves this way. When I prepare utensils in the kitchen, they don't jump back into drawers the moment I turn my eyes away from them. Microsoft Word also won't delete your last paragraph, if you Alt-Tab before saving the document.
On multiple occasions this caused me to start the timer with an unintended value.
Is there a way to get the old behaviour back?
If I understand correctly, you change the timer, but don't hit start, then switch away and back and you see it reset to the last successful (mine reverts to 19:00) timer value?
But, to answer your question: no, there's not a way to get the old behavior back within the app.
This was willfully done this way, probably due to another customer's Feedback submission. Observe that the process is the same when you activate Control Center and press and hold on the timer icon to change the time.
https://www.macrumors.com/2023/10/04/apple-stops-signing-ios...
Following the release of iOS 17.0.3 earlier today, Apple has stopped signing iOS 16.6.1, iOS 17, and iOS 17.0.1, preventing iPhone users from downgrading to any of those software versions.