Vicious circle - cannot open apks anymore without Amaze. I would install Amaze, except that I can't open its apk

[lklaus]

Right now I’m not at home, so I’ll have to do this later. But maybe you could do it like written here: Fairphone Open 17.06.4 (Android 6.0) release

Lp: lollipop
Mm: marshmallow