About managing attributes in layers created with quickosm in QGIS

I am trying to create layers for each bundeslaeder of germany on railway lines, with the key: railway and the value: rail.
The problem is that when I create the layer, it doesn’t let me export it because in the attributes table there are some of them that give problems.

Apart from this, I would like to combine the layers to create a general one but since there are many attributes in each one, it gives me problems, or maybe the problem is another one.

I am working with it to look for suitable areas for solar panel plants and the data that really interests me is the number of rails that there are per track line, since the ones that matter are the ones with two rails. What is the attribute that dictates this, so that I can keep it and eliminate the rest, and so that I can make a good union of layers.

Also, how can I quickly identify or filter/program in some way to be able to see the two-rail ones?

Thanks and I hope for your quick answer as I am quite lost with the program.

I finally resolved that problem.

Now I have another one which is basically that I create a layer and I enter in the attribute table for deleting the columns that I am not interested in, but the program starts loading features instead of deleting them. Do you know how can I solve this and create a layer after all with maybe only 10 columns in the attribute table?