Sign in to YouTube
Click your profile picture
Select YouTube Studio
In the left menu, click Content
Select the video you want to make private
Click Visibility
Choose Private
Click Save
To make your channel less visible, go to Settings in YouTube Studio
Click Channel
Open Advanced settings
Turn off the option to show your channel publicly if available
Hide your subscriptions and saved playlists in YouTube settings if needed
To fully remove public access, delete or unlist all videos and playlists as needed