USB & MIDI: Everything you need to know to get it right (USB MIDI Host vs Interface explained) - YouTube
MeeBlip cubit duo: USB MIDI interface and MIDI thru | meeblip
USB 3 Camera Adapter,3 in 1 USB Female OTG Adapter with Charging and 3.5mm Headphone Audio Jack Splitter for iPhone/iPad,Support USB Flash Drive,MIDI Keyboard - Walmart.com
MIDI Thru 1in -> 10out splitter PCB or a Kit from Deftaudio on Tindie
MIDI Thru 1in -> 4out splitter PCB or a Kit from Deftaudio on Tindie