Why does my Mac not see my external drive as a boot option unless connected via an Apple-branded dongle I'm running into this odd issue where my external drive (Windows 10, Bootcamp) will only appear as a boot option if connected via the Apple dongle, and not via my regular off-brand dock/dongle. 

Odd thing is, it works even if I connect the drive to the Apple dongle, then to the off-brand dongle, but not if I connect it to the off-brand dongle directly.

I've managed to boot from it (holding Alt/Opt on start), but that was with it connected directly to the Mac with the Apple-branded dongle. 

I'm on an MBP 16" 2019
Why does my Mac not see my external drive as a boot option unless connected via an Apple-branded dongle?


Low quality USB bridge.

Inside the dongle, there's an IC (integrated circuit) that bridges the USB bus on your computer with the peripheral device.  Off brand manufacturers look for every edge to increase their profit margin so they use components that aren't exactly up to par. 

Personally, I'm very wary of plugging in an off brand, low cost peripheral device into what is the highest priced laptops/desktops on the market today.  

There was a time when USB cables were being made so poorly they could actually kill your device.  This is why you go with reputable brands.  I'm partial to Anker (they make an equivalent to the Multi-Port AV Adapter) because they offer an 18 to 24 month warranty on all products.