QB4c4462323b64193cb638nr314nz1843m46mrf2zjkc#
Longest individual notation?

Since some chess websites use ++ instead of #, you could argue that Qa1xe4++ is the longest
++ is used for double check, and of course a Queen move cannot be a double check.

Wait, can you add 1-0 to the end of your post?
Like, Qd7xe6#1-0 without space
No
I think the longest is dxe3++e.p. 8 non-period characters. (Chess.com doesn't write double check or en passant, but this does)
Maybe dxc6e.p.+, I guess?
dxc8e.p.=Q+ maybe?
Almost quite! Except that en passant captures don't happen at the seventh and eighth ranks.

actually if you had doubled pawns on the file you could actually write something like c7xd8=Q#
No.

maybe if you manipulate the board so this could happen, it could be like
2372. exd8e.p.=Q#1-0 (20 including spaces and periods, 18 without periods, 17 without space or periods.)
including some methods like move number, en passant, 1-0 (win) and pawn promotion?

if you manipulate the board, you could probably get en passant on 8th rank
chess.com lets you manipulate the board and the rules.

maybe if you manipulate the board so this could happen, it could be like
2372. exd8e.p.=Q#1-0 (20 including spaces and periods, 18 without periods, 17 without space or periods.)
including some methods like move number, en passant, 1-0 (win) and pawn promotion?
You can't have an en passant on the 8th rank. Also, you could increase that number from 2372 to 237200.
So true
I think you can do Qdxe8++ , checkmate
*Qdxe8#