Tente isto:
Abra um terminal
Pressione Ctrl + Alt + T
Execute:
exec sudo -i
nano /etc/apt/sources.list.d/opera-stable.list
No arquivo que é aberto, cole este texto:
# This file makes sure that Opera Browser is kept up-to-date
# as part of regular system upgrades
deb https://deb.opera.com/opera-stable/ stable non-free #Opera Browser (final releases)
Ctrl + O
Salve o arquivo.Ctrl + X
Feche o nano.Continue correndo no terminal:
wget -O - http://deb.opera.com/archive.key | apt-key add -
apt-get update
apt-get install opera-stable