Save as eml to nextcloud not working anymore

[alabre]

Describe the bug
Mails were not saved in nextcloud when I select "Save as eml in nextcloud"

To Reproduce

1. Select an eMail
2. In the burger menu on top right choose "Save as eml in nextcloud"
3. Click "Select" on any folder/subfolder shown in the dialog to choose the targed folder

Expected behavior
When I check the target folder the eml file should be there, (or an error message written into the nextcloud logs). But there is neither the one, nor the other. (And no message in apaches error log file, too). BTW: When I select download as eml file all works as expected.

Please complete the following information:
Nextcloud 25.04 on PHP 8.1 on Archlinux
Chromium, Firefox browser checked under linux and windows

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