can GlassWire See all the activity that happens on my pc? or is there apps that can slip without me knowing?
GlassWire accesses a Windows API that should show all network activity. Nothing is perfect but in most normal cases GlassWire should show all your network activity.
I guess theoretically there could be some type of sophisticated malware that somehow accesses the network in a way Windows itself cannot see, but I have not heard of that happening so far.