Filelink doesn't work on thunderbird linux

I use windows and linux systems. The windows version can upload and share files. The linux version can not upload any file. The setup works. I get the data of my quota. So setup is correct.

Have anybody an idea?

Which Linux and Thunderbird versions do you use?
For me it works on Ubuntu 18.04 (64bit) with Thunderbird 60.8.0.
Can you see and errors in the Nextcloud log?