If you offered that to Lyon they'd just say fuck off. They don't need money and they have a bunch of wonder kids potentially leaving for huge fees so Ndombele sticking around for some continuity is great for them.
And having just turned 22 his price is only going to go up, and big clubs are always going to want top midfielders. United need a couple, PSG would love him, Real Madrid need to revamp their midfield in the next 18 months.
They're also in the Champions League still, and having already beaten us, there's no reason they should doubt themselves against a Barcelona side that's as bad as it's been in years.