I tested the Apple Lightning to USB 3 Camera Adapter (MK0W2AM/A) with an iPhone X. A SSD Drive won't mount, even with external power. But a USB A 3.0 flash drive will.
News] External ssd does work on iPhone : r/iOSBeta
LaCie-Rugged-BOSS-SSD-iPhone-App - LaCie Blog
Super-Fast SSD Flash (200MB/s) Coming This Year. iPhone and iPod touch Price Cut?
New report suggests new iPhone may have 3GB of RAM - GSMArena.com news
Anyone Having Success Getting A External HD To Work With IPad OS? - MPU Talk
9to5Toys Last Call: upgrade iPhone 4 to VZW 6 for free, iPhone 6 cases from $5.60, Samsung 250GB SSD $110, more - 9to5Mac