Hello this is related to a recent post:
https://community.esri.com/t5/arcgis-experience-builder-questions/experience-builder-filters-not-displaying-values/m-p/1568884#M16545
In my case, the Filter type 'Is any of' will build in the Filter expression builder config, but the multi-value pick list control is then not displayed in the widget itself:

And then here in form element selector, no choices appear:
I don't think this is a new issue. I can tell you for this experience all of the layers from my webmap data source are from enterprise 12.0 portal hosted distributed collaboration feature layers.
So I'm at a loss...
here's a working copy:
https://experience.arcgis.com/experience/1ee9cb0cb8a040c0b634a712ab9baca9
@JeffreyThompson2
@TonghuiMing