MacBook Pro M1 lags with external monitor Samsung M8

Hello Mott1986,

Welcome to Apple Support Communities!

We want to help make sure your software is working normally so your cursor is not lagging.

Use these steps first:

"If your Mac runs slowly

If you find your Mac is running slowly, there are a number of potential causes that you can check.

• Your computer’s startup disk may not have enough free disk space. To make disk space available, you can move files to another disk or an external storage device, then delete files you no longer need on the startup disk. macOS can also help you optimize storage by storing files in the cloud and helping you identify files you no longer need. Choose Apple menu  > System Settings, then click General in the sidebar (you may need to scroll down). Click Storage on the right, then click the storage recommendations you want to use. 
• An app you’re using may require more memory than your Mac has easily available. You can use Activity Monitor to see how much memory your Mac and apps are using. See View memory usage in Activity Monitor. Also see the documentation that came with the app to find out its system requirements.
• Quit any app that isn’t compatible with your Mac. For example, an app may require a different processor or graphics card. See the documentation that came with the app for information about its system requirements.
  • To see what processor your computer has, choose Apple menu  > System Settings, click General  in the sidebar, then click About on the right.
  • To see which graphics card your computer has, choose Apple menu  > System Settings, then click General  in the sidebar. Click About on the right, then click System Report. Click Graphics/Displays to see the name of the graphics card installed your computer.
  • Quit any apps you’re not using.
  • If you have problems with your disk, use Disk Utility to verify and try and fix any issues."

This Apple Support page has the full details: If your Mac runs slowly - Apple Support

We hope these steps can help isolate and resolve the issue so the Mac is performing normally again.

Cheers!

Hi Mott1986,

Let's continue with trying some other troubleshooting steps. Test this issue in another user account. This will tell us if it's a universal issue or related to just the one user account. To set this up, follow these steps:

1. On your Mac, choose Apple menu  > System Settings, then click Users & Groups  in the sidebar. (You may need to scroll down.)

2. Click the Add Account button below the list of users on the right (you may be asked to enter your password.)

3. 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 the computer or change settings. To give the user permission to access your shared files or screen, you may need to change options in File Sharing, Screen Sharing, or Remote Management settings. See Set up file sharing and Share the screen of another Mac.

For more information about the options for each type of user, click the Help button in the lower-left corner of the dialog.

4. 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.

5. Enter a password for the user, then enter it again to verify. Enter a password hint to help the user remember their password.

6. Click Create User.

7. 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.”

• Select “Allow user to reset password using Apple ID.” To use this option, the user must have set up iCloud on this Mac. However, this option isn’t available if is FileVaultis turned on and set to allow the user to reset their password at startup using their Apple ID.

• Use Sharing settings to specify whether the user can share your files and share your screen.

This information is from Add a user or group on Mac.

Take care.

Hi Mott1986,

Contacting Apple Support is the best path forward to resolve this issue. They will be best equipped to address this:

Contact - Official Apple Support

Cheers!