Where are downloaded mail attachments stored?

When I click on an attachment in my mail (Fastmail), I get the option to download it to my file storage (‘bestandsopslag’ in Dutch) - cf. Screenshot 1.
When I select that option, I see a folder with subfolders and files - cf. Screenshot 2.
Yet, when I save the attachment, I cannot find it. In fact, I cannot find any of the folders shown in screenshot 2. Not even when I do a search on specific file or folder names.
When I use the foldes app (‘bestanden’ in Dutch), the Downloads folder is opened (Screenshot 3), but from there, I cannot go to that folder. I’ve manually searched all folders that are shown in Screenshot 4. Also, I connected the phone to my computer and used the Windows explorer to search for the files. To no avail.

Can anyone help me find this folder and the files shown in screenshot 2?

Screenshot 1

Screenshot 2

Screenshot 3

Screenshot4

What happend if you try in screenshot 2 to make a new folder (nieuwe map) first?
Or in screenshot 4 tap on ‘Recent’?

Just tried that. I created a new folder in screen 2 and saved the attachment in there. Again, neither the folder nor the attachment is nowhere to be found. Not with the Files-app (‘bestanden’) and not via Recent in screen 4…
It’s a miracle. Or?

Can you check in the settings of the app Fastmail where the downloads are stored?

I found that the files in screenshot 2 are not on my phone. Fairphone stores them in the cloud.
Problem solved. Thanks for your suggestion @Lidwien