Prevent users from signing into Microsoft 365 accounts that aren't a part of our tenant.

[HelloSkyler]

Many of our users have a Microsoft 365 account with the company that we do business with. The account is used to access a catalog but they are not licensed. This has caused problems when users sign into their Office applications with the wrong account and they can't figure out why their applications don't have full functionality. I would like to find a way to prevent our users from signing into Microsoft 365 apps (Word, Excel, etc.) with their other account. We are using Entra AD and Intune. 

[#2]

@HelloSkyler 

See you are looking at this?

Use tenant restrictions to manage access to SaaS apps - Microsoft Entra | Microsoft Learn

[#3]

@Kidd_Ip Our user's need to be able to sign into the third party Microsoft account through the browser to access certain sites. From my understanding, it seems like these tenant restrictions would prevent them from signing into these sites as well. I just want to restrict them from signing into the Office desktop applications. Thanks for your input. I look forward to your response.