i see now ... To join the Office Insider program, you must have a subscription version of Office. A subscription to Office delivers the latest features on an ongoing basis. If you see 2016, 2019, 2021, or LTSC in the license name, this indicates a perpetual (non-subscription) version of Office. A perpetual license includes features that have been tested and shipped at a point in time; it doesn’t change until the next perpetual version of Office is released. Because this version of Office does not get feature updates, you won’t see the option to join the Office Insider program.