Too bad if you decide that you want a muggle job after all…
Muggles who end up studying at a magical school must be somewhat talented enough to have been invited. (I still think it's somewhat a mind boggle as to how one would convince muggle parents that their kids should end up studying in a school that they cannot see…that's for another time though.)
As we know, they study various subjects that are [unfortunately] not offered in typical schools in the muggle world — defence of dark arts, divination, potions, transfiguration, charms and many more. Not all students are as gifted as Hermione for someone that had not been in touch with magic since birth. So what happens when you turn out to be less than average in your magical school grades and decide to pursuit a muggle profession? How would they keep up to date with current affairs and important events that we deem as common knowledge? Must everyone who studied magic must end up with a magical career?
Surely you cannot use magic to obtain a job and make your CV look better than others and fake qualifications. I doubt the ministry would approve of that appalling use of your skills learnt from their world. Though if you wanted to be a scientist after all, I don't believe that you would know atomic numbers and equations, also high level of mathematical knowledge for that - because with the use of supernatural skills, those are not necessary whatsoever.
It appears that there are not a grand selection of career choices in the reality where witches and wizards belong:
Shopkeepers - Pub with butterbeer, joke shop, magic equipment…basically whatever is at Diagon/ Knockturn Alley, depending on how shifty you are.
Sports people - Quidditch player, gnome throwers? Referees, commentators…
Games expert - Wizard chess champion?
Authors/writers - for magical publications like books, Newspapers…etc.
School workers - Teachers, groundskeeper, whatever Mr Flinch really does.
Then everyone else just either works for the ministry unless you are a death eater /criminal /thief or unemployed.
So I suppose the moral is…study hard??