We have two okta accounts setup one for MM as Web Application and other one for SPA. Do we have any solution to use one Okta clientId which help to generate token for SPA via Okta user authentication with username and password and for MM clientId + client Secret?
A Single Page Application (SPA) within Okta will not have a Client Secret, as a Public client app is unable to secure a secret. Thus, only Implicit flow and Authorization Code flow w/ PKCE are supported for SPAs.
Client Credentials flow (which I assume you are referring to here) requires the use of the Client Secret (and again, should only be implemented somewhere that is able to ensure that the client secret is secure (e.g. you should not be making client-side/AJAX requests to get tokens using this flow).
Within Okta, only Web and API Services apps support Client Credentials flow.