You can view Word .docx files by single-clicking the document and pressing the space bar (Quick Look). In Big Sur, Apple has departed from previous macOS releases by removing the Preview application from the Finder's right-click, Open with sub-menu, but if you launch Preview, you can open (read-only) Word .docx documents.
If it is a properly formed Word .docx, I have never had an issue with LibreOffice (any version) over the years opening these, whether from the Open with sub-menu, or by drag and drop of the document onto the LibreOffice icon in the Dock. I am presently using LibreOffice v7.0.4.2 and it opens a variety of current and aged Word .docx documents.
Even TextEdit will open Word .docx documents, though as it is not a proper word processing application, the formatting will disappoint.
Apple's Pages can open Word .docx documents simply via the Finder Open with sub-menu, by drag and drop of the document onto the Pages Dock icon, or via the Pages File menu open dialog. Pages translates the Word document into its own internal (.pages) format, leaving the original Word document unchanged.
And if you had Office 2008/2011 or the 32-bit variety of Office 2016 for Mac installed prior to the Big Sur upgrade, these Office Suites are unsupported, (and retired by Microsoft). The 32-bit/64-bit issue does not affect your Office documents though, and if you prefer to use a currently supported Office suite, Microsoft has their Microsoft 365 (subscription) and Office 2019 for Mac (single-purchase) solutions available. The Microsoft 365 license can be had through the Apple Online store, and the respective applications from the Mac App Store application. The Office 2019 for Mac package can also be purchased via the Apple Online Store or for less money at Amazon.