Youtube Thumbnail's PNG file is over 2.0mb

No. it's not that kind of problem.

Downloaded png file is 2mb, but very slightly bigger than YT's 2mb standard. It needs fix.

YouTube's recommended thumbnail dimensions are 1280 x 720 pixels. If the image you're creating is larger than than, then try the Adobe Express Quick Action for Resize Image to reduce your PNG's dimensions. Making its dimensions smaller should also reduce the file size.