Update MacOS to allow successful download of Microsoft Office

Need to find how to update MacOS to compatible version to allow successful installation and no restrictions with installing apps or programs (**At present the current operating system version will not allow me to install the MICROSOFT OFFICE 365 package downloaded via the Microsoft website and available installation from paid subscription.

The issue relates to the following Apple product - purchased online via e-bay as a second hand/refurbished unit (unfortunately you don't always get what is advertised or paid for here in when purchasing restricted to within Australia with Covid-19 & International Border Restrictions).

Hardware Overview:

 Model Name: Mac mini

 Model Identifier: Macmini3,1

 Processor Name: Intel Core 2 Duo

 Processor Speed: 2.53 GHz

 Number of Processors: 1

 Total Number of Cores: 2

 L2 Cache: 3 MB

 Memory: 4 GB

 Bus Speed: 1.07 GHz

 Boot ROM Version: MM31.00AD.B00

 SMC Version (system): 1.35f1

 Serial Number (system): YM***9G6

 Hardware UUID: CB78586F-1AF0-5258-BBAB-409636776434

DOES ANYONE KNOW A SOLUTION OR SHOULD I JUST CONTACT APPLE TECHNICAL SUPPORT DIRECTLY?? Urgently needing this issue resolved as it is interfering with job applications and video conferencing etc.

Please help BECK... ??

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