Building NXP QN9020 firmware on GNU/Linux?
It appears that the QN9020 has a Cortex-M processor core. It is certainly possible to develop software for a Cortex-M using a gcc cross-compiler running under Linux. I've done this for other NXP ARM processors many times.

It appears that the QN9020 "mini DK" development boards have a dedicated J-Link interface so you should be able to use any generic SWD debugging interface. The J-Link is a good one.

So, it looks like it is possible to develop your code under Linux. Having said that, there may be a significant amount of effort involved in creating all of the support libraries and include files for your particular device. It would be a great learning experience....good luck!