Keycloak works for Office365 but fails for SharePoint Online

Getting advice
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4

So you definitely do NOT want to add it to External Identities, that is what was breaking mine.

I used some of the info from here: Azure AD Connect: Use a SAML 2.0 Identity Provider for Single Sign On - Azure - Microsoft Entra | Microsoft Learn

Basically you open powershell and use: Connect-MsolService
Then set up the federation

This is what mine looked like

$dom = "[DOMAINNAME]" 
$BrandName = "[BrandName]" 
$LogOnUrl = "https://[KeycloakURL]/realms/[REALM]/protocol/saml" 
$LogOffUrl = "https://[KeycloakURL]/realms/[REALM]/protocol/saml" 
$ecpUrl = "https://[KeycloakURL]/realms/[REALM]/protocol/saml" 
$MyURI = "urn:federation:MicrosoftOnline" 
$MySigningCert = "[KeycloakSigningCert]" 
$Protocol = "SAMLP" 
Set-MsolDomainAuthentication `
  -DomainName $dom `
  -FederationBrandName $BrandName `
  -Authentication Federated `
  -PassiveLogOnUri $LogOnUrl `
  -ActiveLogOnUri $ecpUrl `
  -SigningCertificate $MySigningCert `
  -IssuerUri $MyURI `
  -LogOffUri $LogOffUrl `
  -PreferredAuthenticationProtocol $Protocol

I’m going to try to write up the whole process, but if this doesn’t get you working, let me know.