Does a draw on the board need to be declared before the time flag is reached? I was participating in a FIDE-rated blitz tournament a while back (15+0, if it matters for the rules), and had finished my match, and was watching another board. White had about 10 seconds remaining on the clock when black moved a pawn which put the board into position of a stalemate (blocking the forward progress of white's only free-to-move pawn). The white player failed to realize in the 10 seconds that they didn't have a move (there were still a few pieces on the board, some pinned, others just blocked, so it wasn't immediately apparent).
I saw the position was a stalemate right away, but neither player recognized it, and since white's time ran out, black took the victory and reported it. In this scenario, should I have:

Notified the arbiter of the discrepancy
Accept the fact that white effectively surrendered by shaking hands and accepted the defeat
Notify the players directly (before anything is reported) and let them resolve it themselves?

As well, would the stalemate stand even if the timeout was hit, or must the players acknowledge a stalemate for it to count (regardless of white's inability to move).
This was undoubtedly a draw. FIDE rules, emphasis mine:

5.2.1 The game is drawn when the player to move has no legal move and his king is not in check. The game is said to end in ‘stalemate’. This immediately ends the game, provided that the move producing the stalemate position was in accordance with Article 3 and Articles 4.2 – 4.7.

So the game was over, and it was a draw. No player needs to claim or acknowledge or anything. That the clock was still ticking and everything else was irrelevant as far as the rules were concerned.
(there is also another rule that would apply, a flag fall is only a win for the opponent if he has a series of legal moves that lead to checkmate, and here he clearly didn't -- but it's moot because if you don't notice the stalemate, you don't notice this either)
Now, the problem is that no player noticed the stalemate, so they didn't realize what the actual result of their game was. So of course they didn't ask an arbiter either.
What you, as a spectator can do is always very hard to say. As far as the rules are concerned, you hardly exist, and if you do the rules only want you to stop interfering.
But in this case, the game was over. There was no danger that you would distract the players, nor was there any way for you to influence the result anymore. In my personal opinion, it was fine for you to walk up to them and point out the stalemate, to prevent the wrong result from being reported. Or alert an arbiter. But maybe others disagree.
One thing that is not the answer is &quot;accept the fact that white effectively surrendered by shaking hands and accepted the defeat&quot;. That happened after the game already finished, so shouldn't influence the result.