Is there any way to extend the refresh token by x more days using refresh token grant type?
Can you share what is the use-case and add little more information which will help readers understand the need & help?
In general some guidance on expiration & usage of oauth policies.
https://docs.apigee.com/api-platform/antipatterns/oauth-long-expiration
https://docs.apigee.com/api-platform/reference/policies/oauthv2-policy