Hello @Wendy Heijnen ,
if you have a Microsoft 365 subscription or a non-subscription version such as Office Home and Business 2021, 2019, 2016 or 2013, you cannot run these versions together on the same computer in most cases.
However, there is one exception: If one of the two products was installed via MSI (common practice for volume license products), you can run both in parallel.
Install earlier versions of Microsoft 365 first. For example, install Office 2010 before installing Office 2021, Office 2019, Office 2016 or Office 2013. This also applies to other products from the Microsoft 365 family, e.g. Visio, Project or Access Runtime as well as language packs and proofing tools. If you do not install Microsoft 365 in this order, you may need to repair the later versions of Microsoft 365. Information can be found here: How to use Office 2013 suites and programs (MSI deployment) on a computer that's running another version of Office: https://learn.microsoft.com/en-us/office/troubleshoot/office-suite-issues/use-multiple-versions-of-office
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