I have Opera on 2 different computers with completely different hardware parts in 2 different homes and i still have the same issues, Very sluggish and slow especially with a lot of tabs opened. I dont have this same issue if i still to the older v77...only any version after that. I am not the only one to report this. I think there was some large changes to the browser / engine after v78 and v80 etc, Its so much slower especially a decent amount of tabs.
I have since gone back to v77, but i encountered an issue, you cant go backwards with your profile intact, so for some reason it just doesnt keep track of passwords on my v77 after i went back from v82. Even when i disable and enable password manager etc, it just doesnt work at all. But its so much faster than all the versions after v77.