I bought a refurbished Mini 2 from the DJI official eBay store. The controller needs to be calibrated every time it is turned on. Is this normal?

No, I'd say that is not normal. I've only needed to calibrate my RC-N1 controller once in over a year.

That's definitely not normal.  Sounds like you have a defective RC. I'd seriously consider returning.

Hello, waya81. Thank you for reaching out and we're sorry for the inconvenience. If the remote controller frequently prompts to calibrate, please refer to the following steps to troubleshoot:
1. Avoid touching the joystick/wheel during the boot process.
2. Check whether the rocker/ wheel is stuck or loose.
3. Remove the joystick and reinstall it.
4. If you wear magnetic jewelry on your hands, please take it off and observe.

Hope this helps. Please keep us posted. Thank you for your support.

Somewhere between checking these steps, and the new firmware update, the controller is no longer beeping constantly now. I don't have time at the moment to make sure everything is still working correctly with the drone itself, but I will update if there are any problems.