In some cases such as a Ryzen machine with AMD card installed in 1x slot (connected to platform chip not CPU) you can get boot hangs on Antergos where the main USB option will get stuck on the splash screen. If you select the vesa fallback you will see endless errors. (for some reason on a real install these aren’t a problem)

The solution is to turn iommu off just during the install, then turn it back on afterwards for VFIO related setups.
Note that with a USB3 flash drive on a modern system it should only stay on the splash screen for 1 or 2 seconds at most.