how to repair mac freezes on insufficient app memory?

Use the Activity Monitor application and make sure to use View >> View All Processes 

What process or processes are using the Most CPU  and Memory.

Often times,  the issue maybe a combination of Processes

When the computer is using so much CPU / Memory,  it can be an indicator of a Lack Of Empty Space on the Drive.

In which case, the CPU and Memory usage would become much more because it is searching for Empty Space to save all the Changes the user is performing.

To check the amount of Free Space versus the Used Space

Finder >> Go >> Utilities << Disk Utilities

What does it report as in below image

You are welcome

Firefox or Safari or another other Web Browser

How many Web Browser tabs are in usage.

Each tab may have content that is consuming great amounts of CPU / Memory 

There could be some third party software installed and used on this computer that consumes a lot or RAM

To avoid a session of Q&A, Q&A  and Q&A  

Download the Application Etrecheck ( External Link ) directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid for added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - >>>> using the Additional Text Icon  <<<<