the task is difficult because there is no money to spend
the budget is very limited and therefore this makes the task very difficult
in his previous experience, coach Allegri did not hurt, this time he has more difficulties due to lack of money
Maybe Allegri can still give a good result at the end of the season with their current & additional players. But, their focus can be on the Coppa Italia or to be in the Top 4
(if juventus can't make their performance better). I think Ronlado's departure at a time when football was only able to give a permission for spectators going to the stadium after Corona made it a little difficult for Juventus to get funds. Transfers made at beginning in the season did not meet Allegri's expectations. And I remembering how Allegri find difficult times after bringing AC Milan get a Serie-A Title. After that, the performance of the Milan players went down and Allegri become get fired.
I think he actually did arrange the team quite well but the problem is some players became injured. Right now the situation is very challenging for Juventus. Only 3 wins out of the 8 matches are just not enough.
I agree with @masulum that the departure of Cristiano Ronaldo actually had a substantial effect on the performance of Juventus. And recently Paulo Dybala has also left the club. There has been a further weakening of the team's attack as a result of this.
If a coach doesn't acquire the team that he is looking for, it will always be difficult for him to find success as a coach. Right now I think the managerial position of Allegri is under a lot of threat. I think he will be given a little more time. But two things have to happen. Juventus need to improve their performance quickly so that they can finish at least in the top 4 at the end of the season. If either of these things does not happen he is almost certain to get sacked for sure.
For Dybala I agree with you, but for Cristiano Ronaldo not so much. He had never been very close to the team, it seemed to me just a commercial operation.
In any case, if players leave and do not arrive it is a signal of a "monetary" problem, as I have always said.
This season Allegri has to work in reserve, with a team with low morale.