Airdrop does not work with my iPhone 6s

I have an iMac 12.2 (27 inch, Mid 2011) upgraded to 32 Gb Memory and a 1 Tb Crucial SSD. It works perfectly except for Airdrop with my iPhone 6s.

Airdrop on the iMac works perfectly with my old iPod (5th generation). Now my question. Can I change something on the iMac that has anything to do with Airdrop? Bluetooth card? Wifi card? Or anything else.

Here in Germany, every shop I've visited or called wants to sell me a new Mac. I also have a MacBook Pro (17-inch, Early 2008) with the known graphics bug. Again, the usual suspects wanted to sell me a new MacBook Pro. But I removed the LogicBoard 2 years ago and baked it in the oven. It has worked flawlessly since it was reinstalled. Just like the graphics card on my iMac. I've had it twice in the oven 4 years ago. But since the new software fan control, the iMac has been working perfectly again. Except for Airdrop. It must be because the iMac has Bluetooth ver.2.1 + EDR and the iPhone Bluetooth 4.0 or 4.2.There must be some hardware to change.

My iMac runs with High Sierra.

I did it everything by myself an with a little help from my iFixit Tools and Videos.

Thanks to you all.