Depending on where you normally check your Outlook inbox (on the web, or on the desktop application), the "environment" is dictated by both your Operating System version (either Windows OS or Mac OS), along with the version of your Outlook application.
These environments use what is called an "internal browser", which means the browser version that the Outlook application itself uses when connecting to certain external products, including the Groove Outlook add-in. The internal browser of your Outlook application is not the same as your "default browser" that opens when you click links from Outlook. It is internal to the Outlook application itself, and cannot be changed via settings.
The general rules of thumb are shown below. If you are using Outlook on:
Outlook application for Windows: the internal browser for newer OS/Outlook applications combinations is Microsoft Edge, where Groove is 100% supported; the internal browser for older OS/Outlook combinations is Internet Explorer 11, which is a browser that Microsoft has stopped supporting, and therefore Groove also cannot support this environment
Outlook application for Mac: the internal browser is Safari, where Groove is supported 100%
Google Chrome (web-based Outlook): the internal browser is Google Chrome, and the version is based on your Google Chrome version. All Google Chrome versions are 100% supported by Groove, so no need to worry about compatibility if you are using Chrome to visit your Outlook inbox/calendar
Microsoft Edge (web-based Outlook): the internal browser is Microsoft Edge. Groove is supported in Microsoft Edge versions 79 and above
To check which internal browser your OS/Outlook versions support, please check this guide from MSFT.
If your environment (the Windows OS version + Outlook app version combination) supports Internet Explorer 11, you will see an error message like the one below:
In this scenario, you would need to upgrade your environment to be supported by Microsoft Edge as the internal browser for your Outlook application. This may entail working with your IT team to upgrade either your Windows OS version, your Outlook application version, or both. This guide contains all the details as to which OS/Outlook versions you'd need to upgrade to in order for the internal browser to be Microsoft Edge.