I think theres two primary formations, one when you are playing a weaker team you expect to attack a lot. The other when you are playing a team where you expect to defend a lot and hope to pick one on a counter or something.
The team when you face Bournemouth
Pickford
Patterson - Coady - Tarkowski - Mykolenko
Iwobi - Gana - Onana
McNeil - Calvert-Lewin - Gordon
One more midfielder than a back 5, Patterson can get up and provide width while McNeil tucks inside, and has more time and space against a weaker side to hit passes. In essence Gordon and Patterson provide the width here, Myko hangs back more, and behind DCL Iwobi and McNeil end up pushing in.
The team when you face Arsenal
Pickford
Patterson - Holgate - Coady - Tarkowski - Mykolenko
Gana - Iwobi
Gray - Calvert-Lewin - Gordon
You add in one defender, attackers except for DCL drop in to help defend, The key is you want solid defence and then a quick counter attack, so while Gordon and Gray help out defensively, you then use their speed for a quick counter especially on anything DCL holds up. While McNeil has good defensive workrate I dont think hes ideal for this setup unless you have the lead or really expect to rely on Gordon and DCL for counters. You could also add back a midfielder, and just leave Gordon and DCL up top.
For the most part your new bench is Begovic, Coleman, Mina/Holgate, Garner, Doucoure, McNeil/Gray, Maupay, Vinagre, Allan