I’ve had this issue before. When you select the ROBLOX studio window, click the render window too and the paste button will highlight showing that you can paste (assuming you copied a model from another instance of Studio)
Actually my problem lies in with the script editor. I can’t paste simple words from Google Chrome to the scripting window, yet I can copy characters from Studio itself and paste them just fine.
Are you focusing the script editor by clicking it before pasting, or are you just alt+tabbing into studio and pressing ctrl+v? It might be similar to what I mentioned in that you have to focus the script editor first before you can paste anything into it. If not, that’s an annoying bug.
Could be something to do with copying HTML or something, and roblox not converting it to plain text? Because if you copy say parts of a webpage into like MS Word, it copies the sizing and everything, which leads me to believe it could be something to do with that.