(I'm not here to debate whether or not it is)
Too late! Your interpretation of FIDE rules is in error. The capture is not an obligation.
FIDE Rules 3.7d
A pawn attacking a square crossed by an opponent’s pawn which has advanced two
squares in one move from its original square may capture this opponent’s pawn as
though the latter had been moved only one square. This capture is only legal on the
move following this advance and is called an ‘en passant’ capture.
It says "may" capture the Pawn, not "must" capture the Pawn. There is no obligation.
It says "is only legal on the following move" meaning that the possibility of capturing en passent only applies for a single move, after which the opportunity expires. It does NOT say "is the only legal following move", which might be how you mis-read the FIDE rule.
I'm sure this has been discussed at some point but I would like to hear opinions regarding it. To open the discussion I would first like to state that axiomatic to this question is the idea that en passant is in fact a forced move (I'm not here to debate whether or not it is) and going by fide rules it is.
The question is simple if by moving a pawn forward 2 squares you engage a pawn in a way that it must capture by en passant and by doing so the pawn moves to a new spot uncovering a check on the King, is the initial pawn move actually a checkmate. E.g. White moves a pawn forward, black is forced to capture and the white rook now has a direct line to the king and it is white to move.
It would be a rare occurrence but if there is no contingency for this in the rules I believe it would be a legitimate and quite frankly beautiful checkmate however I could fully understand that since en passant is not possible without exposing the king it could also be considered a stalemate. (And would in fact be an interesting way to force stalemate).