Dear Ivan Lekhnych,
Good day!!
As per the description shared, I understand the problem where the the Azure DevOps add-in is disabled in the Excel app. Since it's a custom add-in that needs to be installed, I suggest you to refer the troubleshooting KB: Resolve Azure DevOps Office integration issues
If the problem persists, please contact Azure DevOps Service Support for further investigation.
Thanks for your understanding.
Regards,