I have the same problem in highlighting text, on a wacom tablet ,, However using the right button on the tablet pen I can highlight text then copy and paste as needed but this is more awkward. The pen stylus seems to be acting as a scroll wheel for a mouse.
The same problem occurs with the Chrome browser,, so maybe it's the chrome code in opera is causing the problem.
As other browsers are working fine

@moebiusopera I have the same problem when using a old wacom tablet and now it stopped working with Windows 10.
So today I bought a new tablet, which is working with Windows 10, however you can't use the pen pointer to highlight text, you have to use the right click button on the pen.
You can use the pen pointer on other browsers to highlight text, then to copy and paste using the left click button on the pen