You need to update your WhatsApp version to the 2.19.110.20 iOS and 2.19.298 Android beta updates to receive this feature. Also, a new invite system has been introduced, so if someone chooses except the ‘Everyone’ option in Group Privacy and at that time if someone wants to add you in a group then you will get an invitation to join the group which you can accept or deny.

Steps to Enable the Feature (Android):

• Open WhatsApp
• Tap on 3-dot menu on the top right corner
• Visit the ‘Settings’ option
• Tap on ‘Account’ then ‘Privacy’
• Scroll down and then tap on ‘Group’
• Now select one of the three given options — Everyone, My contacts, or My contacts except…
• After choosing tap on ‘Done’

Steps to Enable the Feature (iOS):

• Open WhatsApp
• Visit the ‘Settings’ option in the bottom bar
• Tap on ‘Account’ then ‘Privacy’
• Scroll down and then tap on ‘Group’
• Now select one of the three given options — Everyone, My contacts, or My contacts except…
• After choosing tap on ‘Done’

These new privacy settings will be available worldwide in the coming weeks.
WhatsApp, April 3, 2019.

I didn’t know that “comings weeks” = “more than 6 months” why did they write that if they didn’t enable the feature yet.. https://t.co/EhkQjbsb1k pic.twitter.com/PVNjPocznI

— WABetaInfo (@WABetaInfo) October 21, 2019