failed to create portal near end dungeon

currently on my map I have 2 portals for the nether, both were created thanks to found default portals.

I wanted to create a portal near the end dungeon so when I am ready to kill the dragon I don't have to go the long way that I am currently

and I was surprised that when creating a portal for that area, when trying to enter the portal to go to the nether, it teleports me to the location of my first created portal.

I tried to creatively create portals in other biomes and if I could create them