"Extract Shapefile Encoding" not showing shapefiles

[dgva]

Describe the bug
When trying to search for a shapefile layer, in order to work with the tool, the file type filter is locked to "*.shp", but it does not show any shapefiles. If the path is directly written in the bar, however, the tool gets the shapefile and runs as usual. But it is impossible to see and select shapefiles in this explorer. In the image below, it is possible to confirm that there are shapefiles in the folder, but they don't show in QGIS. I have tried with other folders, but the problem is still there.

How to Reproduce

1. Try to run the tool "Extract Shapefile Encoding"
2. Click on the dotted button, to search for a shapefile
3. Go to the desired folder
4. The shapefiles do not appear at all

QGIS and OS versions

QGIS version	3.16.7-Hannover	QGIS code revision	0471743
Compiled against Qt	5.12.8	Running against Qt	5.12.8
Compiled against GDAL/OGR	3.0.4	Running against GDAL/OGR	3.0.4
Compiled against GEOS	3.8.0-CAPI-1.13.1	Running against GEOS	3.8.0-CAPI-1.13.1
Compiled against SQLite	3.31.1	Running against SQLite	3.31.1
PostgreSQL Client Version	12.6 (Ubuntu 12.6-0ubuntu0.20.04.1)	SpatiaLite Version	4.3.0a
QWT Version	6.1.4	QScintilla2 Version	2.11.2
Compiled against PROJ	6.3.1	Running against PROJ	Rel. 6.3.1, February 10th, 2020
OS Version	Linux Mint 20
Active python plugins	quick_map_services; db_manager; processing

Additional context

Other tools work as usual, it seems to be restricted to this tool. In another computer, with Linux Mint 20.1, QGIS 3.18, the problem is also happening.

[gioman]

Confirmed on master/KDE, but is ok on 3.16 on Windows.