Assuming you've found a reliable source for the compressed version of Microsoft Office 2021, here's a step-by-step guide to downloading and installing the software:
Downloading a "highly compressed 10MB" version of Microsoft Office 2021 is not a safe or legitimate practice
To help you find the best solution for your needs, could you share:
Google Docs, Sheets, and Slides offer seamless collaboration online. To help you find the best setup, tell me: Do you need to use the software completely offline ? What specific tools (Word, Excel, etc.) do you use most?