Go to Analytics - https://analytics.google.com, analytics accounts and choose the account you want to set up GA4 for.

After you select the account, you will see this page. You want to choose 'create property'. 

You will then want to fill in the 'Property Name' with the name of the account you are working with. Click Next for the next step. 

Fill in the 3 options, industry category is 'internet and telecom' , business size - small and the last option 'Measure customer engagement with my site or app'.  

The last step is to select 'web.' 

This page will pop up to let you set up a data stream. 

Enter the URL of the account you are working with, and then in the stream name, the name itself including GA4.  Click ' Start Stream'. 

This is the page you will see appear, you need to copy the measurement ID. 

The stream is now created and you should see this page. 

You then need to head back to google tag manager. search for the account you are working with and click the blue link so it takes you to the page. 

Once you have selected the account on GTM, make sure you are on the tags section. 

Press New, and you will see this page.