Some moments become priceless immediately after you realize they cannot happen again.

Some moments only reveal their value once you know they cannot recur. The last time you did something with someone, an ordinary afternoon in a period that has now ended, a routine you did not know was temporary. It is not possible to identify these in advance, and trying to would make life unlivable. It is possible to be a little more present in general.

Rather than attempting to identify the important moments, practise being in the ordinary ones. Put down the phone for the small routines with people you love. That is the whole of what can be done about this, and it is enough.