Should we go for a commercial product ( nginx , Red Hat OpenShift API
gateway) or an open source spring cloud gateway would suffice ?
Open-source version of Kong will work also.
i would suggest to check & read this article first : https://medium.com/@harsh.manvar111/api-gateway-identity-server-comparison-ec439468cc8a

You can check for the Kong API gateway once, as it supports authentication & authorization with API key along with options like OIDC, JWT, and many plugin supports.
As you don't require a developer portal otherwise there is a good option Konga.
Kong is very lightweight and in the background runs on the Nginx platform has verities of the plugin supports also and good community support.
There is also a plugin for logging & monitoring you can attach or enable them use them and Kong will forward the data to the central log system.
People also use Kong at edge & service mesh internally for mtls and networking if required.
we been using Kong for a long and have written some good articles on Kong & keycloak also if you are using Keycloak IAM. : https://faun.pub/securing-the-application-with-kong-keycloak-101-e25e0ae9ec56
You can also check out basic setup of Kong & Konga : https://faun.pub/kong-api-gateway-with-konga-dashboard-ae95b6d1fec7
Kong installation : https://docs.konghq.com/enterprise/2.5.x/deployment/installation/docker/
There is also another API gateway called : https://wso2.com/api-manager/