My kobo doesn't work with the update to Big Sur

I have bought myself a Kobo e-reader. Until the last update of my macbook air, it worked without any problems.

Last week I have updated my macbook to Big Sur.

Since then I can't download any books to my e-reader anymore and it isn't visible in finder.

He's connected and he's loading, but that's it.

How can I fix this problem?

I can't find any helpful information on the internet.

Thank you.