Hi:
Below is the link to the service manual.
HP ENVY x360 15m Convertible PC Maintenance and Service GuideIMPORTANT! This document is intended fo...
Chapter 5, page 35 has the size screw you need for the M.2 drive standoff.
Phillips s PM2.0×2.4 broad head screw broad head screw.
It's going to be hard to find the exact one. See if a local PC repair shop has one they can spare or sell.
Otherwise this kit should work.
Amazon.com: M. 2 SSD mounting Screws Kit for Laptop and Nvme m.2 ssd (Screw fit Laptop): Industrial ...
The screws are just a tad too long (3mm, vice 2.4mm), if there is zero tolerance in the screw size, but they come with washers.
So you could put a washer under the SSD (between the SSD and the standoff), and that should take up the extra space.