Here is the VUP reference sheet and it is referring to the striker safety return spring as the one that was removed. All new post VUP 320's, in '19 did not have that spring, and had all the newest upgraded parts.
TXPO
ColdBoreCustom.com
Certified Glock Armorer
Certified P320 Armorer
Certified M&P LE Armorer
If Glock had developed something like this it might of been our new military pistol instead of the Sig 320.
https://youtu.be/sh_vyzOGLkI?si=gHnorP9rMniGN3i9