You need to gather requirements. Planning to get acquired? Bootstrapping and want to preserve runway? Where are your apps currently? What IdP is already in place? Do you have an existing IdP in place (AD?) that you want to preserve as your source of truth? What apps need SSO? Are they third party or self hosted? Do you need MFA? Are all users full time employees?
A keycloak or zitadel instance may meet your technical requirements (something you can confirm in an afternoon or two.) But if you’re about to have new corporate overlords through an acquisition or a large corporate client, Okta may be the path of least resistance.