I solved it by copying the link addresses from the cleaner and limiter in the sidebar (by pressing right mouseclick and clicking on the copy address) and then pasting those URLs into an empty tab search bar. Pressing enter and then pressing ctrl - to make the zoom level lower than my standard (which is 125% because I have a big monitor and my screen is far away). Which made the zoom level lower for the sidebar cleaner and limiter as well.
@Merulox ... I'm successfully listening to music now on Last.fm, using the latest update of the Opera GX browser on a MacBook Pro (running OS 10.13.6 , High Sirerra)
š¤ Good luck! š¤