The best thing to do is to make a screen for the admins

No, the problem doesn't lie in learning an outfield position.
At the moment, most people train their players by having them play in outfield positions, and I don't think that's forbidden.
For example:
L. Islas
L. Carvallho
M. Bajracharya
K. Abakar
P. Barboza
W. Kleff
Ect...
I think the problem that created this was the position changes during the match

When you say "most people", I don't think we have the same definition of the word "most"

But the fact is that there are optimisations, not to say flaws, in the training with the goalkeeper/outfield player position inversions and that there have been automatic settings (perhaps not very 'happy' ones) that have been programmed to counteract this.

But in fact I see two main problems

A word only has meaning in its context. Here, the subject is the loss of a goalkeeper's characteristics, and some people thought this was linked to learning another position... I simply wanted to show that this was not the cause, with examples of players who have mastered several positions without encountering this problem.
You've now touched on other points that could be the subject of a separate debate, with popcorn and cold drinks so as not to mix everything up, as an old footix proverb would say... 😉

C'un bug car la autre gardien du manager canard et coriger

It would have been credible if the player had been improving, but he hasn't been since this new season