1. Right-click twice
This is the most common reason. YouTube replaces the right-click menu on its player with its own (Loop, Copy video URL, Stats for nerds). Right-click a second time in the same place and Chrome's menu appears with Picture in picture.
2. Start the video and wait for the ad
Picture-in-picture needs a playing video. Before playback starts, or while an ad plays in a separate player, the option may be missing or the window may close when the ad ends.
3. Use the media controls button
When a tab plays media, Chrome shows a music-note button on the right of the toolbar. Click it and press the picture-in-picture icon. This bypasses YouTube's menu entirely.
4. Update Chrome
Open chrome://settings/help, let Chrome install any update and click Relaunch.
Picture-in-picture bugs are usually fixed in updates.
5. Turn off extensions that modify YouTube
Ad blockers, theme changers and player-enhancing extensions sometimes replace the video element. Open the video in a guest window (profile icon → Guest) where extensions are off. If picture-in-picture works there, turn your extensions off one by one to find the cause.
6. Check policies on a work or school computer
Administrators can turn picture-in-picture off. Open chrome://policy and look for
policies about picture-in-picture or video. If one is set, ask your administrator.
7. Use another way to start it
If the right-click menu is the problem, Youtube Pop Out Player adds a pop-out button to the YouTube player and a keyboard shortcut — no right-click menus involved. It uses the same picture-in-picture window, so if picture-in-picture is turned off by a policy, it will not help. See how to pop out a YouTube video.