In past decades wasn’t WT teaching that the “modern fulfillment” of this fleeing to the mountains was Fleeing ,to, taking refuge in God’s Kingdom - the Mountain of Jehovah (Micah 4 :1,2)..?
Yes,, I believe that's right.
There are two types of reliance on "mountains" the WT org has mentioned. In both cases, "mountains" are claimed to be associated with earthly organisations. On the one hand, God's Kingdom - and the earthly expression of it in the form of the JW Org and its congregations - are seen by WT to be the "mountains" that "righteous ones" would flee to.
In contrast, the "worldly ones" would call upon human "mountains" to try to protect them in the end - any sort of human organisations separated and alienated from God. Obviously, those "mountains" would not provide the needed protection. They use Revelation 6:15-17 for this:
Then the kings of the earth, the high officials, the military commanders, the rich, the strong, every slave, and every free person hid in the caves and among the rocks of the mountains. And they keep saying to the mountains and to the rocks: “Fall over us and hide us from the face of the One seated on the throne and from the wrath of the Lamb, because the great day of their wrath has come, and who is able to stand?"
Isaiah 2:2 was also used to contrast these two types of mountains: "“And it must occur in the final part of the days that the mountain of the house of Jehovah will become firmly established above the top of the mountains" God's organisation supposedly represented by JW Org becomes "established above" other organisations. One WT from the 1980s I just looked up said:
"The symbolic mountain of Jehovah’s pure worship is becoming more prominent, so that meek persons can see how it contrasts with the sectarian “hills” and “mountains” of Satan’s permissive world. They “get out” of false religion and flee in growing numbers to Jehovah’s mountain of worship"
That's how I've always understood the Org to interpret these verses and the symbolism of "mountains".
It doesn't surprise me that they're "refining" this to increase emphasis on listening to and obeying the GB (to know which "mountains" to flee to), since that's the way everything is going now in their teaching.