I have installed the update opera mini 11.0.1912.96480 on Lollipop 5.1
It is still not possible to select the external sd card as download folder.

download to external sd card not possible

When I select any external place the Button "Ordner wählen" (select Folder) is disabled

Other Apps like QuickPic can write to the external card.
The App TotalCommander needed an Update and works now.

My Smartphone BQ Aquarius M4.5 Buildnumber 1.2.0-20150907-2010
Lollipop 5.1
Opera Mini 11.0.1912.95711

Greetings from Cologne
Harald