I just happened to install that same image today with no issues. You have some corruption going on from somewhere. Common causes are sdcard, not properly unmounting the sdcard after burning and bad download with the image. Some sdcard has a tipping point at 32G not burning properly. I have had a bad etcher version at one time. You might try unpacking the Manjaro-ARM-xfce-rpi4-20.12.1.img.xz image and use dd to put the Manjaro-ARM-xfce-rpi4-20.12.1.img on the sdcard.