He is on €8,5M-10M after tax per year. That’s a guaranteed £260-305k per week. But if you add the tax benefits of moving to Italy he’ll be earning much more.
For exemple his sponsorship deal with Adidas is worth 5M/year. His Instagram account earns him similar numbers.. On all this moving to Italy means he can pay a fixed fee of €100k/year instead of the 20% flat tax in the UK.
Well his after tax income in the UK would equate to about €10.8m per year, so going by your numbers he's actually taking home less?
Also, United are a bigger pull follower wise than Juve, which would equate to better deals for Pogba, so probably best not to involve individual sponsorship deals with regards to wages his club pays.