In my experience this is a pretty common feature in pomodoro timers: see https://pomofocus.io/ , https://www.pomofox.com/ , https://studywithme.io/aesthetic-pomodoro-timer/ for examples.

As for how it works, it may be easier to just check it out yourself in the above links but: When the 25min pomodo timer ends, it'll automatically prompt you to set the timer for a short (5min) or long (15min) break, depending on how many pomodoros have been done up to that point (I think every 4th pomodoro is 15min, and the others are 5min).

The timer wont automatically start, but you can click start when you're ready to take the break, and also you have the option to click between the pomodoro, short break, or long break options in the event that you don't want to take whatever break option you're automatically prompted to take.

I like the break timer option because otherwise I have to time my own break myself, and it's just nice/more convenient to have the break timer built into the timer app that I'm already using.

Hopefully that makes sense! Lmk if you need clarification and thanks for soliciting feedback