I found one of those gray market key vendors and bought a Office 2021 Professional Pro key for less than $20. It came promptly and even included a link to a Microsoft download site. (Don't rush to download.)
I don't need all the included Office apps. The legacy installation dialog would let me choose which application and features would be installed. I used to use that dialog to omit all the Office apps except Word, Excel, and PowerPoint.
But now Microsoft has an Office Deployment Tool that lets you customize the installation.
I recalled the solution I had found earlier and revisited my previous post.
The referenced site, MS Guides, seems to have gotten crossways with Google and probably other organizations. I used archive.org to retrieve the instructions. This post is my recap of the process and is heavily based on MS Guides.
Step 0: Uninstall all the Click-to-Run Office 365 apps that come pre-installed.
Step 1: Download the appropriate version of the Office Deployment Tool from Microsoft. Use Google to find the proper download and download it.
Step 2: Double click the download to extract the contents of this file. It will create a new folder with configuration files (xml) and setup.exe.
Step 3: Tailor the following code as needed and paste it into a new text document.
<Language ID="en-us" />
<ExcludeApp ID="Access" />
<ExcludeApp ID="InfoPath" />
<ExcludeApp ID="Lync" />
<ExcludeApp ID="OneNote" />
<ExcludeApp ID="Outlook" />
<ExcludeApp ID="Project" />
<ExcludeApp ID="Publisher" />
<ExcludeApp ID="SharePointDesigner" />
<ExcludeApp ID="Skype" />
<ExcludeApp ID="Skypeforbusiness" />
<ExcludeApp ID="Groove" />
<Display Level="Full" AcceptEULA="TRUE" />
The above sample code will only install Word, Excel, and PowerPoint.
Then save this as config.xml in the folder created earlier.
Step 4: Copy the code below into a new text document file.
cd /d %~dp0
setup.exe /configure config.xml
Then save this as install.cmd in the folder created earlier.
Step 5: Double-click on the install.cmd file and it'll run. You may have to right-click on it to run it as an administrator. I didn't have to do this.
The process will even download the required bits.
Step 6: After successfully installing Office, launch one of the apps. You'll be prompted to login OR enter a product key. Enter your new product key there.