I already said that if Lo Celso and Ndombele are in the same team then 4-3-3 is the best option.The solution is to start playing our best players, not changing the formation which fits one player, who is our 10th or 11th best player.
A MF with PEH-Lo Celso-Ndombele is what is by far the best option for us. If Lo Celso and Ndombele are not fit enough to play every game then bring in similar players in January who are.
Moura and Lamela can start in Europa and should never see another starting spot in the PL as long as Bale and Bergwijn are healthy.
Dier is complete garbage but going to play so not worth addressing as Jose will never drop him.
Reguilon has been great, by far our best signing. He is among, if not the, best LB's in the league. He is a true FB and there is zero need to move him to LWB, as he has zero issues playing as a traditional LB.
A move to a 3-5-2 means we are taking off better players to put worse players on. That makes little sense.
However, if Jose doesn't trust them to both start, I think 3-4-3 or 3-5-2 is something we can try out.
You say Reguilon is a good LB, but I think there's untapped potential. Bale started out as a LB too.