I have a Button on QuoteLineItem object, which call Visualforce Page. It's related list button and, as far as I know, it can't be an Action - only Buttons supported on this object. So the issue is that this Button is displayed both in Lightning and Classic, and I need it only in Lightning. Is there some way to remove button from Classic page?
When you create a custom button, you need to add it to the layouts separately for classic and Lightning.
For Lightning, you need to add button in Salesforce Mobile and Lightning Experience Actions and for the classic, you need to add in detail section.
As you want the button to be visible in Lightning only, Just add the button to Salesforce Mobile and Lightning Experience Actions and remove the button from the detail section.