Lovera, on 2022-December-01, 03:19, said:
But with a strong hand and particularly with a 5♠-5♦ the fourth suit (3♦) is expected to jump bid (see Fourth Suit Forcing by Liversidge in Novice and Beginner Forum #26 n.2).
You can hardly call North's hand strong - well, I certainly can't given the potential misfit, and that South has limited his/her hand by the rebid of 2
♣. I am hazarding that very few players, even British ones, play 4SF as invitational these days, preferring the GF version.
I openly admit there will be hands where using 4SF as an unconditional GF will result in a poor contract, but that's no different than making a game force in the 2/1 system. Anyway, a player has to use judgement here, and it is normally the responder who has set up the GF who dictates where the contract is headed. With any 'forcing to game' bid there is also an opportunity to bail out below game level if you feel the hands are not fitting well and will not produce a game. But that is as rare as hen's teeth.
If you do not use 3
♦ as a splinter here but to show a 5
♠/5
♦ hand instead, I would expect something like
♠AKxxx
♥x
♦AKQxx
♣xx not a watery
♠AQxxx
♥Q
♦Qxxxx
♣Ax where the second suit
♦s is as good or better than the first mentioned
♠s.