I want to see only the glyphs with Unicodes in the font view. Is there a plugin or script for this?
Create a Smart Filter with Has Unicode set to Yes. Clicking on the gear icon in the lower left o the Font View to Add Smart Filter. Then you can select that filter to only show glyphs with Unicode values.
See section 7.5.4 Smart Filters in the Glyphs 3 Handbook which can be found on the Learn | Glyphs page.