Happened to me a few years ago - it turned out my mouse had a tiny piece of fuzz in the left button that caused an occasional glitch. You can hear the left button click when you’re going to type in a box but it really didn’t enter because one doesn’t usually look. Be sure to actually look in the typing box to see the cursor blinking then you are OK - at least in my case.
BTW, I love Opera and have using it for almost 20 years across all my devices. Also if you haven’t tried the ‘V7 Notes’ for an extension do so as is it fabulous. Haven’t tried the AI interface yet, we’ll see. Also in many cases for fellow HTML geeks I use that “inspect element” extension to often go around a paywall, ad blocker, cookie editor etc. are handy also.