Inverted fullbacks has its own advantages and disadvantages. I will try to explain how lucas can help up deal with this situation.

Thread-

So first of, what is the role of inverted fullback?
Inverted Full backs are used when the wingers like to cut inside. They move the ball centrally and slot themselves as the third midfielder when having the possession of the ball. Pep did it with bayern and city

The Inverted full-backs help the creative midfielders to play with freedom. They support the line of attack.The inverted full-back protects the counter-attacks from taking place. They sit ahead of the two centre backs and number 6 depending on the lineup

The centre of the pitch is where most of the position is won. With inverted full-backs slotting in as another midfielder it helps in winning the possession back when it is lost. There will be an extra player in the centre of the pitch which helps in winning back position...

Disadvantages-
The problem for inverted fullbacks will arise is they face up against a traditional winger . the type who gets their head down, bombs for the by-line, then whips in a cross. The fullback will be forced to defend on their weaker foot which is never good.

Since they like joining the attack, the likelihood of them offering an overlapping run for the player in front of them is cut dramatically. This can pose problems as the opposition can double up when defending against the winger playing in front of the inverted fullback.

I still think lucas should play there instead of kimmich cus of what kimmich brings to our midfield is irreplaceable. Keeping it as rb is like using 20% of him.