Adding a WFS layer with filter for non-existent attribute leads to broken layer

[pathmapper]

Describe the bug
Adding a WFS layer with filter for non-existent attribute leads to broken layer:

• no checkbox to toggle visibility available (instead there's an image icon displayed)
• removing the filter or updating the filter (filtering for an existing attribute) has no effect

How to Reproduce

1. From the QGIS top menu: Layer -> Add Layer -> Add WFS Layer ...
2. Add connection for: https://www.wfs.nrw.de/geobasis/wfs_nw_dvg
3. For Layer DVG1 Kreise und kreisfreie Städte build the following query:

SELECT * FROM nw_dvg1_krs WHERE GN = 'non-existent-attribute'

4. Add layer
5. See error --> broken layer was added to the layer widget

QGIS and OS versions

QGIS version
3.20.0-Odense
QGIS code revision
decaadb
Qt version
5.15.2
Python version
3.9.5
GDAL/OGR version
3.3.0
PROJ version
8.0.1
EPSG Registry database version
v10.018 (2021-04-02)
GEOS version
3.9.1-CAPI-1.14.2
SQLite version
3.35.2
PDAL version
2.3.0
PostgreSQL client version
13.0
SpatiaLite version
5.0.1
QWT version
6.1.3
QScintilla2 version
2.11.5
OS version
Windows 10 Version 2009

Active Python plugins
QuickOSM
db_manager
MetaSearch
processing