Once again you are giving guidance to ask a question. If " Azure / SAML Single Sign On" is still not supported for authenticating to QuickBooks Online please make that statement and then provide the guidance for asking a question of Intuit Developer Support. It is clear from what I am seeing that "Azure / SAML Single Sign On' is still not supported. 

Over 720,000 organizations use Microsoft Entra ID (Azure / SAML Single Sign On). Most accounting firms and bookkeeping organizations utilize Microsoft Entra ID. It is embarrassing that Intuit has not been able to provide this feature that would help enhance some of their most critical customers with the enhanced security and seamless login they are trying to access. 

Simply pushing organizations to a single vendor (Google) is not the solution! This not only puts an undue burden on orgs that use Microsoft Entra ID is their default and sole SSO tool but also forces them to compromise their security if they don't use Google. These organizations have Conditional Access policies surrounding Microsoft Entra ID and having to complicate with Google is not right.

Please supply a response as to why this feature is not getting implemented.

As respectfully as possible Jonah, OIDC is only supported for developer apps.

OIDC is not supported in any way to authenticate an end user's direct access to their company files through QBO website or the QBO desktop application. 

The issue here is enabling support for external identity providers for end user access to their QBO native company files. 

It is clear that the overwhelming majority of the users posting here are asking if Single Sign-On (SSO) with Office 365 or Azure Active Directory is available for authenticating directly, browser-based to https://qbo.intuit.com. This is so their end users can simply use a browser such as Microsoft Edge that has pre-authenticated with Microsoft Entra ID (Microsoft Azure SSO) to https://qbo.intuit.com/ and gain access to their QBO user account.

It has nothing to do with developer third-party applications connecting to QBO.

The majority of large vendors have all accomplished this. An over-simplified example is browsing to a vendor's website and having the option "Login with Microsoft 365". 

I don't understand why Intuit can't support this in a simple user-friendly manner? Either add the pre-configured option within the "Enterprise Applications" library of Microsoft Azure like the thousands of other vendors have already done or provide instructions to create a new application within Microsoft Azure "Enterprise Applications" like thousands of vendors have already done.

All the current responses from Inuit are to so-called supported SSO between QBO and a developer's app (e.g. bill). This is not what all the people on this thread are requesting. It is easy to see that. Intuit can obviously see that as they respond to use Google for SSO. But there are likely more orgs on here using Microsoft Entra than Google for SSO and the last thing they want to do is have to support Google SSO for a single product that can't seem to resolve the direct authentication with Microsoft Entra SSO. These orgs have existing Azure Conditional Access policies that would greatly enhance security surrounding their users authenticating to https://qbo.intuit.com/ such as only from Compliant Devices, geo-fencing, trusted IPs, etc.