I am not able to upgrade my MacBook

To add to Leroy's excellent advice, Microsoft supports the latest OS and two previous versions, so that means Big Sur, Catalina, and Mojave. Way down in this Microsoft document

https://www.microsoft.com/en-us/microsoft-365/microsoft-365-and-office-resources?ms.officeurl=systemrequirements%3fms.officeurl%3dsystemrequirements&rtc=1

is this:

If your MacBook Pro is 2012 or newer, your can upgrade the OS. If not, look to the free productivity suite LibreOffice:

https://www.libreoffice.org/discover/libreoffice/

szaid78 wrote:

my current version 10.13.6 is not allowing me to download Microsoft 365

The current Office for Mac; Office 365 or Office 2019 (One-time purchase) are OK with Catalina/Big Sur

To activate a Microsoft Office 365 subscription you simply enter the email address you used when you extend the subscription with Microsoft.


How do I upgrade Office?

https://support.office.com/en-us/article/how-do-i-upgrade-office-ee68f6cf-422f-464a-82ec-385f65391350

compare:

https://products.office.com/en-us/compare-all-microsoft-office-products?&activetab=tab:primaryr1

Office Home & Student 2019:

https://www.microsoft.com/en-us/microsoft-365/p/office-home-student-2019/cfq7ttc0k7c8?activetab=pivot:overviewtab

Office Home & Business 2019: This stand alone includes Outlook—

https://www.microsoft.com/en-us/microsoft-365/p/office-home-business-2019/cfq7ttc0k7cq?activetab=pivot:overviewtab