Glad to see you here in the Community, @magnus1.
I'd like to ensure that you'll be able to import the categories successfully upon importing items in QuickBooks Online.
You'll need to make sure that the mapping of your categories is correct. Having an inaccurate format can be the reason they're not importing.
On the other hand, you can also check the characters used on the categories if they are valid. Here's a link that contains details about the accepted characters that can be transferred in the system: Acceptable characters in QuickBooks Online.
To give you more tips when importing products and services including selecting its category in QuickBooks Online, please see these references:
You can count on me if you have any other questions. Just let me know by dropping a reply below. Have a wonderful week!
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