When choosing "send as email", file attachment does not work on Windows. Therefore, "Automatically open folders of attached files" should be enabled as default. Since "send as email" seems to work at Linux, I would propose to enable this as default only on Windows.
original UI:

UI in JabRef 5.10 (2023):

When choosing "send as email", file attachment does not work on Windows. Therefore, "Automatically open folders of attached files" should be enabled as default. Since "send as email" seems to work at Linux, I would propose to enable this as default only on Windows.
original UI:

UI in JabRef 5.10 (2023):
