Actually the chinglish description of the adapter nowhere says 4K@60Hz
- 4K video resolution requires a 4K capable computer video source, DP cable, and output display.
According to Intel® Core™ i7-7820HQ Processor (8M Cache, up to 3.90 GHz) Product Specifications you need a straight DP connection.
4K support indicates the product's support of 4K resolution, defined here as minimum 3840 x 2160.
Product description on Amazon as well as some of the comments tells it supports 4k@60.
"Resolution up to 4k x 2k (3840 x 2160) @60Hz & @30Hz; Supports Multi-Stream (MST) for daisy chaining multiple monitors and high precision audio such as LCPM, DTS, and Digital Dolby."
"Works exactly as intended and outputs 4k @ 60hz out of my X1 Carbon 5th gen."
"It works 4k 60hz between xps 9560 and Dell S2817Q."
You need to find the bottleneck.
In best case another video, USB-C or TBT 3 driver will help.
In worst case the monitor or the computer (particularly it's BIOS) is the culprit.