ho remove melted plastic on glass?

You could use some ceramic cooktop cleaner. I've got some Cook Top Max for those extreme cases like pellet bags, leggings, etc. Works good. But it cleans everything. I prefer to keep a buildup of glass conditioner on the glass.

I had an old thread on this, I pretty much figured out I scratched it by accidentally grabbing a piece of clinker when using wet ash to wipe the glass. It's a short surface scratch and otherwise still unchanged. Live and learn.

A straight razor would probably work. I have a glass cook top here and the thing sometimes gets messy ad then baked on. I use a straight razor blade scraper to get the bulk off and then cleaner / polish to scrub off the rest.