@CroTeam Company portal is the official MDM client which allows end user to see the applications which have been made available to them and list of devices which are enrolled under their user accounts for Intune with the ability to remove(unenroll) them as well.
Company portal also have many other information like helpdesk contact and website where the end user can reach out in case they need any help. You can read more about it here : https://learn.microsoft.com/en-us/mem/intune/apps/company-portal-app
Windows 10 comes with a in-built MDM client which does the same job as company portal about enrolling the device to Intune when you follow that account settings and enroll the device using this path. But this does not allow users to see List of apps which are made available and whole bunch of other information's about other devices same user might have enrolled.
Its a use per basis, I have seen many customers not using Company portal on windows but many do if they feel the need.
Company portal is mandatory for IOS and Android but optional (depends if you need to have those extra information)
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