I see many sources on the internet writing like there's an agreement between Conte and Osimhen to sell him this summer. It looks like this is really happening however I'm wondering his cost the most.
Arsenal will surely have to pay a gigantic fee.

Most probably with a fee over 100 million euros anyway. Arsenal really needs a star player in forward position. That's a sure thing. However if they spend this much on him, and I don't even know what the details of the contract would be, I guess they aren't planning to make many transfers. Do they need that many transfers though? I guess not as they are already doing just great.
But Arsenal really needed a star scorer (just like Man City has Haaland) to increase their chance for a Premier League trophy.

Situation is currently not clear what happening around with someone saying he is going to stay with Conte for the another season and few reports are saying he is already set for leaving Newcastle United is already offer price of €100m which is rejected by Napoli president and now Arsenal is also having same price tag mean things are pretty unclear about his future because most chances Napoli president will never sell him on this price with he already announces fixed price is €150m, and I don't think any club will go for this price with his performance was also not as he has done when they won title in Serie A.
Arsenal is much needed player like him who will give them leading support at the front for the win of the title, and they will surely try their best for having him into their team, but price is surely problem with next few weeks are going to be important about this all with anything can happen about this transfer.