Why I don't have the specific Opera repository under the tab "Other software"? Will I miss next release updates?
Maybe should I need to insert it?
Opera 45 (newly installed)
Ubuntu 17.04 (64-bit)
Is it a so difficult problem to solve?
Check your /etc/apt/sources.list or any *.list file in folder /etc/apt/sources.d/ for this (or similar) line
deb https://deb.opera.com/opera/ stable non-free
If you do have an entry like this one, you will get opera's updates along with the rest.