I try to use a dual drive go USB Type C on my brandnew MacBookAir, but the Stick is not displayed

Thank you for your reply, Tomi, and for letting us know that didn't work.

Seems Apple recommend a Sandisk USB Flash drive for storage ... along with other storage options .

https://www.apple.com/shop/mac/accessories/storage?page=1&f=flashdrive&fh=3783%2B45ec

Wondering if you might want to take your new MacBook Air (and the USB drive?) into a nearby Apple Store ?

There you may find expert help and advice on both difficulties!

A Genius Bar reservation is recommended:

https://www.apple.com/retail/geniusbar/

Else:

Apple Support has an article online that may help:

If an error occurred while updating or installing macOS

https://support.apple.com/en-us/HT212526

Or

Update macOS on Mac (Update? or Upgrade?)

https://support.apple.com/en-us/HT201541

If needed:

There is a "Get Support" link to Apple at top right on this discussion page.

or

See a list of Apple phone numbers around the world.

https://support.apple.com/en-us/HT201232 

All the best :-)

Hi Tomi57,

Welcome to the Apple Community.

If you are not seeing the stick on the desktop,

you might want to try opening a Finder window,

to see if the stick is listed near the top in the sidebar list.

Cheers :-)