the section is: https://docs.openshift.com/container-platform/4.20/installing/installing_aws/ipi/installing-aws-vpc.html#installation-aws-arm-tested-machine-types_installing-aws-vpc  

all tesed arm instances for 4.18+:
c6g.*
c7g.*
c8g.*  <<<<< -------- Currently missing in our docs -> Tested by the customer -> Works as expected.
m6g.*
m7g.*
r8g.*

We need to ensure all sections include "Tested instance types for AWS on 64-bit ARM infrastructures" section been updated for 4.20+    

Should we consider adding support to 4.18.z and 4.19.z as well?  

4.20.z    

My customer tested installing OCP on 4.20 on c8g instance type and the installation worked as expected. 

Our documentation doesn't reflect support for that instance type yet. Need to add testing in our support matrix for c8g instance type.

Documentation update to include support for c8g instance type.