USCF and FIDE will rule a draw in the following position: White pawns on a4, d4, g4 and king on e1 vs Black pawns on a5, d5, g5 and king on e8. Even though both players still have pawns there is no legal series of moves that can lead to checkmate. A knowledgeable TD/arbiter is needed to make the correct ruling, but if one player flags it is a draw. Chess.com does not look at the "no legal moves leading to checkmate" scenarios and would award a loss to the flagging player because the opponent has what would be mating material against a lone king.
Also, with White having a king on c2 and knight on d3 versus Black having a king on a2 and pawn on a3, if Black flags after White plays Nb4+ then USCF and FIDE will deem it a loss for the flagging player (forced is ... Ka8, Kc1 a7, Nc2#) while chess.com will see the king and knight as not being mating material. If the Black pawn is replaced with a rook then FIDE will award a loss for a flagging player with Black (... Ka8, Kc1 Ra7, Nd3 Ra6, Nc4 Ra7, Nb3# is remotely possible) while USCF and chess.com would call it a draw.
@5
The Laws of Chess are clear:
"6.9 Except where one of Articles 5.1.1, 5.1.2, 5.2.1, 5.2.2, 5.2.3 applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by that player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves."
https://handbook.fide.com/chapter/E012018
However, the Laws of Chess are not correctly implemented on chess sites.
Some positions are won per Laws of Chess, but drawn on the site.
Some positions are drawn per Laws of Chess, but lost on the site.
I can't find an exact source, but I believe that this is because chess.com implements USCF rules on the site. The USCF requires the player have sufficient checkmating material. Thus, while under FIDE rules a K+N against a K+R would be won if the player with K+R ran out of time, this would be drawn under USCF rules as it requires the player at least have an additional pawn or bishop besides the knight.
Chess.com implements something vaguely similar to USCF. The difference between USCF and FIDE is only significant when the player that still has time has K+B or K+N or K+2N (in USCF those are only wins if the win is forced) while in all other positions FIDE and USCF agree. Chess.com does not look at the position. It just ignores all of the opponent's pieces except the king and looks to see if the unflagged player has a pawn and/or rook and/or queen and/or 2B and/or B+N and/or 3N.
If the position is blocked (think K+8P vs K+8P with the pawns locked up in a zigzag fashion and the kings stuck behind their own pawns) then USCF and FIDE would rule a flag as a draw (no legal moves leading to any checkmate) while chess.com would rule flagging as a loss (it only looks at K+8P vs K once the flagging player's pawns are discounted).
That's incorrect. USCF, FIDE, and chess.com all rule a win IFF the player has at least a pawn remaining, even if the player with time has a forced mate. Unless all the other moves are forced otherwise, then it's a draw.