Code test the duration press of the button
Why did the timers stop working?

The main issue seems to be that freeze_timer and btn_timer are of type unsigned int, while millis, as stated in its documentation, returns an unsigned long.

As you may know, unsigned int is normally be able to hold a much smaller range of values than unsigned long. In the case of whatever compiler Tinkercad uses for the Arduino Uno, I checked and unsigned int can hold values from 0 to 65535, while unsigned long can hold values from 0 to 4294967295. Whenever you save an unsigned long into an unsigned int, it will be reduced modulo 65536.

This means that once you pass 65.536 seconds checks such as the (millis() - freeze_timer) &gt;= 2500 will always be true (at least until millis wraps back around after 4294967.296 seconds - around 50 days).

If you would like to learn a bit more about integer conversions, I think this Stack Overflow question covers it.

The simplest solution is, of course, to declare freeze_timer and btn_timer to be of the appropriate type, unsigned long.

Use simpler code

All of the above being said, like Gerben said, the code seems overly complex.

There also seem to be other issues. For instance, I would expect the debounce behavior should not ignore presses that last less than 1 second. Like Gerben said, 10 ms should be enough to discard any bounces.

Furthermore, I think it would be more appropriate to not even discard presses that last less than 10 ms. I would say the debouncer should trigger "press" regardless of whether the press lasted less than 10 ms. It's role should just be to ignore multiple presses within that 10 ms window (although to be fair, ignoring short presses is not a terribly big issue).

Although one could make some guesses, to really help you with this, we would need a description of your intended behavior. What is the purpose of freezing? Is it intended to allow multiple presses to be triggered when you never release the button (or maybe you should wait until release before triggering one again)?