The Data binding Method SAML Plugin setting should be HTTP-POST, you IdP metadata only support HTTP-POST (<SingleSignOnService Binding= "urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"), also check the help of the Client ID field but I bet that Client ID Keycloak field is the same that the Entry ID on the SAML Plugin so you have to enable the advanced setting and set the Entry ID to the same value
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