This idea is simply untrue.
Nowhere does the Bible tell us there will be many converts to Christianity during the Great Tribulation. On the contrary, we are told the peoples will worship the Dragon; Satan and the beast; the Anti-Christ world leader. Revelation 13:3-4
As you say; there will be Christian martyrs, but they will come from the group referred to in Revelation 12:17
We are not told the 144k will convert anyone. From Isaiah 66:19, we are told they will proclaim Gods glory to the nations and the coming Kingdom of Jesus.
You just make such wild claims in order to support the false rapture to heaven theory. Not going to happen, but those who did prove their faith and trust in the Lord during the terrible Sixth Seal event, will receive white robes and will be kept safe during the Tribulation. Rev 12:14
First, Isaiah 66:19 has nothing to do with the Trib. It's entirely an OT matter.
Rev 13:3-4 are about the fake resurrection by the AC, and that unbelievers that will worship the dragon and the AC.
The believers cited in Rev 13:7 are new converts. We know they are new converts because no believers enter the Trib. This is proven in a number of verses. Let's look at two examples: Rev 6:4 and Rev 6:15-17.
In Rev 6:4, no believers would be subjected to indiscriminate murdering. Yet, that's the prevailing environment of kill or be killed.
In Rev 6:15-17, we first see that "everyone" in the world is cited in verse 15. Also in verse 15, clearly in complete terror, everyone hid in caves and among the rocks. Verses 16-17 (NIV): They called to the mountains and the rocks, “Fall on us and hide us from the face of him who sits on the throne and from the wrath of the Lamb! 17 For the great day of their wrath has come, and who can withstand it?”
In Rev 6:15-17,
everyone in the world behaves only as unbelievers would behave. There's an alleged sighting of Jesus in verse 16.
Everyone reacts in complete terror and runs away to hide in caves and among the rocks.
Everyone in the world is involved, per verse 15.
Everyone reacts only as unbelievers would react.
If Jesus were nearby us believers in that same context, we would run TO Him in COMPLETE JOY! We would race to Jesus to THANK AND PRAISE our Lord Jesus Christ!
None of that is seen in Rev 6:15-17 because "everyone" represents the population as 100% unbelievers. There isn't one believer on Earth at the time of Rev 6:15-17.
Rev 6:10 (ESV): They cried out with a loud voice, “O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?”
There you have new converts who became martyrs from the 2nd and 4th seals describing who killed them as "those who dwell on the earth." That phrase, in the context of the Trib, always means "unbelievers who inhabit the earth." This is proven in every use of that phrase in the context of the Trib. Let's look at another example: Rev 11:13 (ESV): and those who dwell on the earth will rejoice over them and make merry and exchange presents, because these two prophets had been a torment to those who dwell on the earth.
There you have two examples of "those who dwell on the earth" as unbelievers.
Keras, you can't prove one believer enters the Trib. All the GM are provably former unbelievers per Rev 7:16 (ESV):
They shall hunger no more, neither thirst anymore;
the sun shall not strike them,
nor any scorching heat.
That was the former existence of all of the GM before they were graciously saved by God Almighty. The wording of Rev 7:16 also spans from the early Trib to deeply into the 2nd half. This is proven true of the early Trib by the words "shall hunger no more." Those specific words relate to "famine" found in the 4th seal (Rev 6:8). The words "scorching heat" specifically relate to Rev 16:9 (ESV): They were
scorched by the fierce heat, and they cursed the name of God who had power over these plagues. They did not repent and give him glory.
Those verses span the time from which all new converts are made in the Trib. This is true because not one believer enters the Trib.