I also had this problem and modifying these 2 files had no impact. gnome-software still launched after Linux startup
Setting below 2 lines in these 2 files had no impact: /etc/xdg/autostart/gnome-software-service.desktop and ~/.config/autostart/gnome-software-service.desktop
Hidden=true
NoDisplay=true
Removing these 2 files also had no impact
I noticed that gnome-software applet was popping up whenever I launched an application installed with snap so it can be related to snap store
I found suspicious location regarding gnome-software in snap-store related folders like this
/snap/snap-store/current/usr/etc/xdg/autostart/gnome-software-service.desktop
Tried to modify or remove that file but couldn't do that even with admin privileges because /snap/snap-store seems to be mounted as read only filesystem according to lsblk command
so the solution might be to remove gnome-software from snap
snap list | grep gnome
snap remove <gnome-software related app>
or to remove gnome-software using apt
sudo apt remove gnome-software*
sudo apt purge gnome-software*
sudo apt autoremove
surprisingly removing using apt somehow also removed this file from snap-store folder
/snap/snap-store/current/usr/bin/gnome-software
which was pointed out in gnome-software-service.desktop file
Exec=/snap/snap-store/current/usr/bin/gnome-software --gapplication-service
After that gnome-software pop-ups disappeared