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.
Also, Kevin Trapp's age is no longer ideal to be Manchester United's main goalkeeper because after all, Kevin Trapp is currently 32 years old. So yes, I am also sure that Manchester United will certainly not sign Kevin Trapp, because I think Manchester United also draw goalkeepers for the long term and not just for one or two seasons. But about Justin Bijlow, I think this could be a great option because after all, Justin Bijlow also succeeded at Feyenoord by winning titles and trophies in the Eredivisie last season. What's more, Justin Bijlow still has a long future so yes, I think this Justin Bijlow can be a good choice for Manchester United for the long term.