You didn’t miss anything: CCP has released minimal data on the mechanics changes related to Invasion Chapter 3 ‘to let players discover for themselves’ or some such silliness.
Nobody knows if Fortress systems will ever stop showing invasion alerts.
You can make yourself actually neutral (white) toward Triglavians by dealing damage to EDENCOM forces - see this thread for discussion and options:
Here is how to gain neutral standings to triglavian npcs
As long as you get your standings into the ‘butter zone’ of positive toward Triglavians and better than -1.0 toward EDENCOM, none of the Invasion NPC forces will initiate hostilities toward you.
Note that personal standings are separate from the security status effects of Liminality systems - while the NPCs won’t attack you, players may do so. Pay attention to sec status changes to avoid gate camps in TrigSec systems.