Generally yes, but the pal here seems to have issues with more than the Dyson. A BT speaker also doesn't work, and I read he can't find and pair any device.
RAC/OPS , please confirm or describe more details. And please tell if you are experienced with all settings and Bluetooth basics or if that's totally foreign land.
The Car connection works, and I assume iPhone and Car have been paired once and still remember each other.
The connection to the dyson doesn't work anymore - or have never worked?
Are any of the devices you want to connect already listed as "known devices" in the BT settings of the iPhone?