See the Configuration section of [HowTo] Install Manjaro on the ASUS TUF FX505DY / FX705DY with Ryzen / Radeon combo. It’s a known/common problem with that WiFi adapter. If you have the means (money and your computer/notebook allows), I’d suggest swapping it out. I have the notebook that post was written for, and I followed the author’s advice and replaced the WiFi adapter and saw about a 30% improvement in throughput. 