Photoshop version 25.3.1
MacOs 14.3.1
In a document with multiple art boards and multiple layers/layer-folders -> select one or more layers and right-click "export as".
The export as window appears as normal. When changing the canvas-size (in that window), both height and width go blank and you can no longer make any adjustments.
This function does work as it should in a photoshop document without multiple art boards.
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