I have read up on this issue as much as I possibly could. I even tried it on the PS4 version of Minecraft and have had no issues with it. I am now trying it on the iOS Minecraft version (which is Bedrock I believe).
So this is the issue:
My current portal (overworld portal) is at these coordinates.
I know the rule is roughly that your X and Z coordinates must be +/- 128 to make it so your portals don't link and you finally get a new portal location. I want a new portal so I can have a better chance at finding a nether fortress.
Therefore I made my new portal at
Z: 900. This obviously is more than the 128 blocks rule, but it still didn't work. I went through the portal, which sent me to the same nether portal that was created from the original overworld portal I made. Am I misunderstanding something? I did the same thing on the PS4 version and it worked normally.