Why is my iPhone 12 Bluetooth constantly buffering?

It's not "buffering". It is looking for devices that are discoverable so that you can pair with them. When you close that page, it will stop. it's like the light in the fridge. It does go out when you close the door...

My Bluetooth keeps buffering saying it is trying to connect with devices

When I open Bluetooth on my iPhone 15, in ‘Other Devices’ the spinning circle is constantly in motion apparently looking for devices to connect to Bluetooth. Ok. But, it’s finding devices that are in perhaps a nearby apartment.. a bit dismaying. I thought I could solve that by pressing on one of the unknown devices. After I did that it said.. ‘Connected’ and moved it into the ‘My Devices’ category. YIKES! So I clicked on the newly added ‘device’ entry and was given options.. I selected ‘Forget this device’.. and it became unlisted under the My Devices heading.. but then promptly showed up again under ‘Other Devices’. I would very much like to have the ability to have those unknown devices not show up again in ‘Other Devices’. I would appreciate an additional option like.. This Device is not mine and I never want it to be in ‘My Devices’ - Never! Can you help with this problem? Thank you. Mary H.

There is no such option. When you open Settings -> Bluetooth, your iPhone will present two lists. My Devices is a list of all devices that you have been paired. Other Devices is a list of all devices detected within Bluetooth range. That range is between 30 and 800 feet, depending on the device. Devices in Other Devices cannot interact with your iPhone in any way unless you tap on one and try to connect.

If you see a device in the My Devices list that you do not want, do as you already did and tap Forget this Device. It will no longer appear in My Devices. If it is still in range, it will continue to appear in Other Devices.