The scenario:

As a developer and designer, I want to know what percentage of users are using mobile versus desktop (focus on screen size) so I can ensure the pages are enabled for our users. 

Requires:

Google Analytics 4 installed

Steps:

Log into Google Analytics 
Go to Explore, choose Free Form 
Title your exploration name
Choose a date range 
Add the following dimensions: Event name, Device category 
Add the following metrics: Total Users, Views 
Tab Settings: 
Technique: Free form 
Visualization: Table 
Segment Comparisons: none 
Rows: Event name  
Columns: Device category
Values: Total Users, Views 
Filters: None 

Considerations:

If you have internal filters, the information will be filtered out.  

Total Users indicates the number of users that have seen the page. 

Views indicate the number of individual page hits. 

Events per session are used to give a general sense of engagement. 

Further data exploration:

You can choose a row, right click and choose “View users“, and drill down to individual users to see where they went after this.  

For the events, you want to look at “page_view” for your information, although you can look at other events for engagement or specific information.  

You can add “Browser”, “Device”, “Operating System”, and “Screen resolution” as dimensions to further see what users are using.  

Remember that when you change an existing report, you are changing it forever. Make a copy or use a new report if you want to explore.