New iMac mini thunderbolt adapter not working with thunderbolt 2. How do I troubleshoot?

Are you sure it's a Thunderbolt display (Lightning bolt icon on plug, no USB cable), not the similar 27" LED display (USB cable, no Lightning bolt icon)? The adapter won't work with non-Thunderbolt displays, even though the plugs will fit.

are you using this adapter?

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?fnode=64aed169270ee0d3de47b9cbe652a975a158a635a86db1da7889c5b35ed9b14dd9fea5feed4e69245c3c860e3996bdcb86fdcad4a3be2949023bf8b19e2185357bba405dce84fb04bb0078917926b8f58c4d754a7479c8bbbad20bce01bfc4b8695720cf62a04ee70901dd311d8067b9

It is working just fine with my M1 MacBook Air and my

Apple Thunderbolt Display.