Hi rythman76,
welcome to the Apple (user-to-user) Community.
Re: "Garageband - can't import files anymore"
If you haven't already: you could try quitting and restarting Garageband,
and, if needed:
Restarting your Mac or device ... will sometimes restore order.
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If more help is needed:
What to do: If an app on your Mac stops responding, closes unexpectedly or won’t open – Apple Support
or
What to do: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
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Else, if you still need help:
Wondering if your are using iPhone, iPad or Mac,
and
which model, which iOS, iPadOS or MacOS is installed,
and
which version of Garageband.
You may need to check the software is updated to the newest compatible versions.
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More info. or support if needed:
GarageBand - Official Apple Support
All the best :-)