Exclude fields in WMS/WFS doesn't show anymore in 3.16

[Gustry]

Describe the bug

In QGIS 3.16/Master, fields which are hidden in WMS/WFS doesn't show in the UI.

Same project opened in QGIS 3.10 and QGIS Master

How to Reproduce

Open the given project in QGIS 3.10 and Master :
tests.zip

1. Make a layer with some hidden fields in WMS/WFS, a project coming from 3.10, or using PyQGIS in QGIS Master.
2. Open vector layer properties, it doesn't show up

QGIS and OS versions

QGIS version	3.17.0-Master	QGIS code revision	7a14973
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	13.0 (Ubuntu 13.0-1.pgdg20.04+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	Ubuntu 20.04.1 LTS	This copy of QGIS writes debugging output.
Active python plugins	quick_map_services; lizmap; plugin_reloader; Mergin; pg_metadata; cadastre; db_manager; processing

I think @3nids you made some changes here, no?

[gioman]

@Gustry if you click on the "configuration" dropdown you get the options to exclude from WMS/WFS

[Gustry]

@gioman As you can see in my screenshot, the "Configuration" is all white, but it should be different, the field configuration is not the same. It should display, at the bottom, some fields configuration in the drop-down already set.

My screenshot shows the same project opened in QGIS 3.10 and 3.16.
The project is in the ZIP.

[gioman]

The project is in the ZIP.

@Gustry this is your project in my 3.16

[Gustry]

@gioman Look my screenshot in QGIS 3.10, on the top.
Some fields are already hidden in WMS and WFS for the last 3 fields.
So the list shouldn't be all white in QGIS 3.16, there should be already some checkbox checked.

Sorry if I wasn't clear, I'm not in front of QGIS ;-)

[3nids]

I'll have a look at it tomorrow.

[gioman]

Sorry if I wasn't clear, I'm not in front of QGIS ;-)

@Gustry no, sorry me as I only got now what you meant, and it was pretty clear.