Update: This is BUG-000185982
Description: Pop-ups in the ArcGIS Experience Builder Query widget fail to display Arcade content when configured using an if statement.
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Original Post:
I'm in the process of submitting a bug report for this and will update this post as I get more info. This is more of a PSA / info gathering exercise rather than a question.
The pop-up in question is composed of a text content block. Inside the text content block is text and various Arcade attribute expressions. The pop-up is viewed in Experience Builder via the map or by selecting a feature via the query widget.
In Map Viewer, the pop-ups are appearing as they always have. Specifically, there is space/visual distinction between the lines boxed in orange:

However, when I click on the same feature in Experience Builder (via the map widget), the spacing is different. It's like they're different lines of the same paragraph rather than individual paragraphs.

Additionally:
The query widget is set to return a feature's pop-up. The query widget now doesn't return the bulk of the pop-up. All of the missing content comes from attribute expressions, but not all attribute expressions are missing (e.g., the waterbody name, Lake Superior, is coming from an attribute expression).

I've had issues before with the query widget, so I tried the feature info widget too since it seems a little more robust. That's returning the pop-up completely as I expect it to look, no weird spacing or anything.