Building/loading some polygon/line layers in the exporter window takes ages

[EricPlayZ]

I have a polygonal layer with around 600-700 features. For some reason, even if I have other layers that are more or less the same in the number of features, this one takes the longest to load, around 15 to 20 minutes. I can't understand why, because even if I combine all of the polygons into one polygon in another layer, that layer takes just as much to load.

I don't have that much time to keep waiting 20 minutes each time I make a modification to something, it's awfully slow. My PC specs shouldn't be a problem:
GPU: RTX 4070
CPU: Intel Core i9-12900KF
RAM: 32 GB DDR5 at 6000 MT/s
2 TB NVME SSD

Why is it taking this long? Isn't there also a way to make the loading asynchronous, so I don't have to wait for e.g. the layer with the buildings polygons to load, before starting to load other layers?

I should mention, I'm using QGIS 3.34.2-Prizren, with the latest version of this plugin 2.7.3.

Below is a screenshot representing the layer I'm trying to load in the exporter.

Need help ASAP, if possible =) Thank you.

[EricPlayZ]

I only now noticed that this happens whenever the layer is rendered as a "Polygon" or "Overlay", instead of "Extruded". With "Extruded" selected, it loads in almost 10 seconds.