Hi @Egbert Steenbergen ,
Welcome to our forum!
As I know, local folder is not supported now in New Outlook. To continue use the "On my computer" folder, I'm afraid that you need to switch to Legacy Outlook.
And when I test to switch to Legacy Outlook>switch to New Outlook I get the following reminder. It's also suggested that you could add your POP account in New Outlook.
Moving back to the old Outlook didn't gave the folders back. The tick for hiding on my computers folder is off.
Do you mean the "On my computer" folder disappeared? If so, please remove add readd your POP account to check if there're any differences.
On the other hand, you can also try to use Time Machine to restore the entire "~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile" folder (assuming "Main Profile" is the profile you are using). For more information, please refer to: Restore items backed up with Time Machine on Mac.
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Hope the above help!
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