Mixpanel integration using server Google Tag Manager might be a good solution if you want to increase page speed and set cookies more accurately.

Mixpanel tag for sGTM can help you with these action types:

• Track - tracks events in Mixpanel.
  
  
• Alias - adds an alias to existing Mixpanel contact. Useful if you need to add a new identifier to the existing user.
  
  
• Reset - resets identification of Mixpanel contact. You can use reset to manage multiple identities on the same device. When a user logs out, you can trigger a reset tag. It will reset the distinct_id and remove existing super properties. Mixpanel will treat subsequent events on the same device as performed by a new user.
  
  

Route data to Mixpanel's EU servers - select if you want to route data to the EU data centers. 

Automatically handle customer distinct_id - Mixpanel server API optimized for stateless shared usage; e.g., in a web application, the same mixpanel instance is used across requests for all users. Rather than setting a distinct_id through identity () calls like Mixpanel client-side libraries (where a single Mixpanel instance is tied to a single user), this API requires you to pass the distinct_id with every tracking call.

Send common data with request - Adds to track request user_agent, path, $current_url, $screen_width, $screen_height, $referrer, user ip, etc.

Get parameters from the variable - select if you want to extract any parameters from the sGTM variable.

Additional Parameters - select what other parameters you want to send and add Parameter Name and value.  

Remove parameters from the request - add parameters that you want to remove from the requests. Helpful in eliminating standard parameters like $current_url or IP.

 Logs Settings - select if you want to use stape logs to troubleshoot your setup.

Useful links:

  1.  Mixpanel tag for server Google Tag Manager.