The general macOS shortcut
⌘ Cmd+⌥ Option+⇧ Shift+V is the shortcut for Edit › Paste and Match Style, which pastes the text using the style of the destination. It works in Safari, Chrome, Pages, Keynote, Notes, Mail and most native apps.
If it does nothing in an app, open the Edit menu: if the option exists, you'll see it there along with its shortcut.
In Google Docs
In Google Docs the shortcut is shorter: ⌘ Cmd+⇧ Shift+V, or Edit › Paste without formatting.
In TextEdit
TextEdit uses rich text by default. To remove all formatting from a document, use Format › Make Plain Text (⌘ Cmd+⇧ Shift+T).
In Word for Mac
Use Edit › Paste Special… and choose Unformatted Text. There are more options in the guide to pasting without formatting in Word.
Make Cmd+V always paste without formatting
In System Settings › Keyboard › Keyboard Shortcuts › App Shortcuts you can create a new shortcut: type the exact name of the option as it appears in the app's Edit menu (for example, Paste and Match Style) and assign it ⌘ Cmd+V.
If the shortcut doesn't work in your app, paste the text in the box above, click Copy plain text and paste it wherever you want: it will arrive without any formatting.