Horrible NVME SSD Write Speeds on M1 Mac mini Only on the USBC Port

Hey there ben1257sb,

Thanks for reaching out to the Apple Support Communities. We understand you're having issues with the transfer speeds when using the USB-C port on your Mac mini, and we'd be happy to take a closer look into what's going on.

To get started, can you let us know if this issue occurs when using a different cable with your external SSD drive? Also, take a look at the steps listed in the following resource that may help with the issue you're experiencing: If a USB device doesn’t work with Mac - Apple Support

If the issue continues after going through the steps above, let's also test the issue in safe mode. Safe mode is a great way to determine whether an issue is caused by software that loads as your Mac starts up. For help with testing the issue in safe mode, and what to do if the issue doesn't occur in safe mode, check out this link here: How to use safe mode on your Mac - Apple Support

Keep us updated on the results.

Have a great day!

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Also: test in a new user account. Same problem?