SEO - Google suggests you can bold words within your Meta Description to make them stand out.
How can that be done in Elements ?
I’m not sure that’s true 
Do you have a link to the docs where you read this?
As far as I know… you cannot bold or style text inside a meta description. Google simply bolds the search terms the user typed when those words appear in your meta description. It’s automatic and has nothing to do with your markup.
Meta descriptions don’t support HTML tags, so nothing you do in Elements (or any builder) will make Google bold specific words. Google decides what to bold based on the user’s query, not the site’s code.
My mistake - Google automatically bolds items within your meta description that match the search terms you gave it … I think : )