My robust broadcom wifi card interferes with my graphic card I have a robust AC1900 Dual band WiFi Card. Its signal is very strong and this causes interference with my AMD RX-650 card, although I had put the cards in as far slots as possible on mainboard. When using the card normally there is no problem. But when using DLNA or AirDrop services, the screen gets a flicker and eventually goes off and on again and is absolutely unusable!
How can I fix the problem without making the card signal too weak and reducing the transfer speed significantly?
I advise you to reduce the card signal level. This won't reduce the speed which is only related to the frequency of the carrier wave and the signal / noise ratio.

This will increase the overall signal / noise ratio of all the hardware using the bandwidth around the GHz (1 - 10 GHz). Net result: the interference should stop below a level to experimentally find. Then the network throughput will be better, but its scope (in meters reached) will be shorter. Most probably you will shrink your network radius from 100 m down to 25 m. You will also lower the quantity of micro-wave heating your eyes and your brain (every thing which is containing a lot of water).