Thanks for the info! Using this method isn't as simple as getting the Savefromnet extension from the plugin store so below I add a short tutorial for lost souls:
- Install tampermonkey extension from the Opera store
- LMB on the tampermonkey icon which has just appeared next to the address bar and choose Get New Scripts
- At the newly opened website choose Greasy Fork
- Search for Savefromnet (I chose https://greasyfork.org/en/scripts/33581-savefrom-net-helper)
- Click on it and click on Install This Script. Finish.
This way Savefromnet won't be visible at the Opera extension bar, but it still works when browsing YT.