Based on community forums (VirtualBox.org, Vogons), here are the top fixes ranked by effectiveness:
Oracle VM VirtualBox is a free, powerful hypervisor, but it was built for modern OSes (Linux, Windows NT, macOS). It does not natively support installing DOS from floppy disk images in the same seamless way it supports an Ubuntu ISO. This is where the humble .img file becomes your best friend. ms dos 622 img files works with virtual box top