Videos on YouTube or other streaming sites show one frame every ten seconds or more only since upgrading Early 2015 MBPro Retina to Monterey 12.6.3 on mulitple browsers (Chrome, Safari, Opera, Firefox). No VPN, no proviate browsing etc.

Hi JustAsking23,

If the issue persists across multiple browsers it may be worth to test in a completely new user.

• Set up users, guests, and groups on Mac - Apple Support

"Add a user

1. On your Mac, choose Apple menu  > System Preferences, then click Users & Groups .
2. If the lock at the bottom left is locked , click it to unlock the preference pane.
3. Click the Add button  below the list of users.
4. Click the New Account pop-up menu, then choose a type of user.

• Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.
• Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.
• Sharing Only: Sharing-only users can access shared files remotely, but can’t log in to or change settings on the computer. To give the user permission to access your shared files or screen, you may need to change settings in the File Sharing, Screen Sharing, or Remote Management pane of Sharing preferences. See Set up file sharing and Share the screen of another Mac.

1. For more information about the options for each type of user, click the Help button in the lower-left corner of the dialog.
2. Enter a full name for the new user. An account name is generated automatically. To use a different account name, enter it now—you can’t change it later.
3. Enter a password for the user, then enter it again to verify. Enter a password hint to help the user remember their password.
4. Click Create User.
5. Depending on the type of user you create, you can also do any of the following:

• For an administrator, select “Allow user to administer this computer.”
• For an administrator, select “Allow user to reset a password using Apple ID.”
• Use Sharing preferences to specify whether the user can share your files and share your screen.

For information about Apple’s privacy policy, see the Apple Privacy Policy website.

If your Mac or Magic Keyboard has Touch ID, a new user can add a fingerprint after logging in to the Mac."

After in the new account, try streaming in Safari and other browsers again. If the issue is resolved, it may be due to specific extensions that are loaded into your browsers. You can see how to check for these in Safari:

• Use Safari extensions on your Mac - Apple Support

Cheers!

Hi JustAsking23,

If you have any third-party anti-virus software running or installed, you can test temporarily removing it. You can also make sure all ports used by apple software are allowed: TCP and UDP ports used by Apple software products - Apple Support

However, there's a possibility it may be a bigger issue. If you've attempted and completed the steps previously recommended by DerekM87 and it continues, reach out to Apple Support directly to further assist.

Contact - Official Apple Support

Contact Apple for support and service - Apple Support

Best.