If you want kill the match then you'd better go for "The Waste Time Tactic" which can be found at the OP.
I don't think that Shield Wall is the best option if you want to kill the match
If you play on a tablet and can't import the tactic then I suggest installing Demo FM18 to your PC and import the PIs from it
Also, the set pieces is a very important thing, don't underestimate it
Pal, you can install Demo Version of FM18(it's free) on any PC around you, import the tactic to see the PIs and TIs and then transfer it to your Switch.
It's very simple :)
Again... have you thought that what a tactic can do has some limits ?
Just try to pick any non-professional club in lower leagues and play against Barcelona's best starting eleven and you'll see that whatever tactic you use you'll be lossing every match by 5-7 or more goals... you can try to...
I also repeat myself once again... have you though that amount of goals conceded and the quality of your players are connected?
Your attackers might be not good enough or it would be better to say they aren't much better than the opposition's defenders which means your attackers lose the ball...
Have you thought that the amount goals you conceded will become lower and lower every time you make improvements to your team?
Just think if it was possible to win every match with default Newcastle team without conceding a single goal then the game would lost any sense because there weren't...