MU has an alternative for onana. Onana was a priority, but it doesn't mean MU shall only focus on him.
I prefer to see MU get one from these keepers, Justin Bijlow or Kevin Trapp.
Kevin Trapp played awfully, Bundesliga clubs easily to humiliated him.
Justin Bijlow played good in Eredivisie, but his recent performance in Euro was not good. But I think your speculation could be right because he's a Netherlands player, it's a privilege as Ten Hag is favor to sign Netherlands player.
If there's no high quality player, then the another option is looking for Netherlands player.
Those could become the last option for manchester united. United could easily sign the new goal keeper as long as it has good monetary but the problem since MU has limited budget. The club can't even afford to buy onana from intermilan.
My choice will be going to the bijlow but MU is now having a new candidate.
Robertz sanchez from brighton gonna be another option. United needs a new goal keeper as soon as possible.
Sanchez's price is still affordable for manchester united. His performance with brighton was quite good last season. Robert sanchez has been also fully experiencing in EPL.
He can easily adapt to the club.