Export Selection messing up with model

Hello everyone! I’m trying to export this model to blender, to make a more optimized mesh

But when I do that some strange holes appear, that doesn’t exist in the original model:

And if I try to fill it in blender it causes ZFighting, so I don’t know how to fix it.

This stuff with Exporting Selection has been causing problems with me for a while, as it was something that worked perfectly fine in the past.

Any solution would be highly appreciated!

(pls don’t come up saying it’s a triangle limit stuff, I know that it is something as much as I know that a simple wedge wouldn’t break that limit.)

Hi, you need to fix it in blender.
2 select the edge and press the F key.
Do ctrl+0 for any corruption. You need to reduce the quality. There is a mistake in the modeling. If not, use a door model.
I hope I helped!