Is it a mod compatibility issue?

No

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

No response

Minecraft version

1.19.3

Describe the issue

So lets say, I want a 19x19 portal connect to a 1x3 portal. And when I ignite the portal, they dont connect. It does it for other people but not me. Is there anything I have to modify to connect big and small portals?

By default, the nether portal will only link to same-shaped same-sized same-direction frame. You can change nether portal mode to adaptive to make it link to other sizes with compatible shape.