I am currently using elasticsearch on aws for m4.xlarge.search what I am trying to upgrade gp2 to gp3 and my question is does it supports m4 instance type referring toc this doc i see N/A for m4 in gp3 table https://docs.aws.amazon.com/opensearch-service/latest/developerguide/limits.html and https://docs.aws.amazon.com/opensearch-service/latest/developerguide/supported-instance-types.html
Yes, you are right!
No gp3 on m4.xlarge.search.
I suggest you switch to a more up to date instance. Is anything stopping you to upgrade to a more modern instance?