I've been using Adblock Plus in addition to the integral Opera ad blocker. I'm not sure which is doing what, but when an ad appears at the start of a YT video I've found that pressing F5 gets rid of it, and none appear while playing. Using an elderly desktop PC.
I might be more sympathetic to Google/YT's pleas for revenue if they weren't such rampant, unapologetic tax evaders.