I suspect that you are missing something. Apple has made three 27" standalone displays:
- LED Cinema Display (27-inch). Model A1316. A 2560x1440 pixel display that takes Mini DisplayPort input.
- Thunderbolt Display (27-inch). Model A1407. A 2560x1440 pixel display that takes Thunderbolt input.
- Studio Display (2022). Model A2525. A 5120x2880 pixel display that takes Thunderbolt 3 input.
You wouldn't use this adapter with the Studio Display (2022) (which would plug into the Mini directly) or with any of the much, much older 15" – 21" Studio Displays (since none of them speak Thunderbolt).
You also wouldn't use it with the LED Cinema Display. The adapter only translates Thunderbolt. It will not make the Thunderbolt 2 side look like a Mini DisplayPort if you plug a Mini DisplayPort into it (the way that a Thunderbolt 1 / 2 host port on a Mac would). To hook up the LED Cinema Display you need a USB-C to Mini DisplayPort adapter; you can find lots of these on Amazon, and they are much cheaper than the Apple TB3-to-2 adapter.
If you are using the adapter to hook up a Thunderbolt Display (model A1407) to a M1 mini, it should work.