
Hi @Y a h y a ,
Which version of the office are you using? Many users said that some same issues disappear after enabling modern authentication ,you can have a try to test if it works.
In fact, every version of Office is different.
Office 2016 and Office 2019 clients support modern authentication by default, and no action is needed for the client to use these new flows. However, explicit action is needed to use legacy authentication.
Office 2013 client apps support legacy authentication by default. Legacy means that they support either Microsoft Online Sign-in Assistant or basic authentication. In order for these clients to use modern authentication features, the Windows client must have registry keys set.
Please refer to this article for more information.
Similar post for your reference:
https://techcommunity.microsoft.com/t5/sharepoint/sharepoint-online-sites-not-showing-up-in-office-365-desktop/m-p/298705
https://techcommunity.microsoft.com/t5/sharepoint/sharepoint-online-sites-not-showing-up-in-office-365-desktop/m-p/1136782
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