Installed Office 2021 but it keeps opening office 365 instead

It seems like the Office 365 app is still set as the default for opening certain types of files, or possibly the system is still recognizing the Office 365 apps instead of the newer Office 2021 apps. Here are several steps you can take to rectify the situation:

1. **Uninstall Office 365**: The first step would be to completely uninstall Office 365 from your Mac. Make sure to back up any data or documents you need before you uninstall the software. You can use the 'Remove Office' tool provided by Microsoft to do this. Once you've uninstalled Office 365, restart your Mac, and then try opening Office 2021 again.

2. **Set Default Applications**: Ensure that Office 2021 applications are set as default for all relevant file types. Here's how to do it:

- Right-click (or Control-click) on the file.
- Choose 'Get Info'.
- In the 'Open with:' section, select the desired application from the drop-down list.
- Click 'Change All...' to set the chosen application as the default for all files of this type.

3. **Update Your Software**: Make sure both your macOS and Office software are up to date. Sometimes, compatibility issues can cause problems with software recognition and default settings.

4. **Repair Disk Permissions**: Sometimes, software issues can occur because of problems with disk permissions. You can use the Disk Utility tool on your Mac to repair these permissions. Please note that Disk Utility's Repair Disk Permissions function is available in macOS versions prior to 10.11.

5. **Contact Support**: If none of the above steps work, you may need to get in touch with Microsoft Support. They may have additional steps you can take or be able to identify a specific issue that's causing the problem.

Remember, the best practice is to only have one version of Office installed on your computer at a time to avoid conflicts like this.

If customer is struggling, they can also find installer links for all the versions of Office here:
https://www.cjs-cdkeys.com/pages/MS-Office-Direct-ISO-Download-Links.html