Load layers for viewing in QGIS 3 from delimited text

Question

I am trying to use part of a script to add points from a delimited text file, however, when I use it the layers are not loaded on the screen and not saved in the path indicated as .shp

import os
import qgis.core

indir = '/home/leo/Área de Trabalho/sle/'
outdir = '/home/leo/Área de Trabalho/sle/'
for root, dirs, files in os.walk(indir):
    for file in files:
        if file.endswith('.txt'):
            fullname = os.path.join(root, file).replace('\\', '/')
            filename = os.path.splitext(os.path.basename(fullname))[0]
            uri = 'file:///%s?crs=%s&delimiter=%s&xField=%s&yField=%s&decimal=%s' % (fullname, 'EPSG:4326', ',', 'field2', 'field1', '.')
            layer = QgsVectorLayer(uri, 'pontos_' + str(filename), 'delimitedtext')
            QgsVectorFileWriter.writeAsVectorFormat(layer, "pontos_" + str(file) + ".shp", "utf-8", layer.crs(), "ESRI Shapefile")
            QgsProject.instance().addMapLayer(layer)

when I do:

print(layer)
<QgsMapLayer: 'pontos_caminho_partículas_3' (delimitedtext)>

In this case, I want to read several .txt files, with coordinates and add these points as shape in QGIS. I am using QGIS 3.10.