Unable to share file in "files" section of general channel

I created a team Family and invited my friend. Now we can chat together on General channel of this team. Unfortunately my friend is unable to see any of the files I uploaded to Files section of this General channel. She also is unable to add any files to this section. The only thing she sees there is a bicycle picture with message -This item not exists or is no longer available-.

I assigned her an Owner permission of this Family team, but it didn't help.

The problem occurs on booth: Teams web app, and desktop app.

What we are doing wrong?