When using clip layers to clip to the outline of a feature in ArcGIS Pro 2.4 the layout and map tabs show results as expected screen grab below.
But when printing or exporting the map the clipping layer is not honored is there a setting I am missing or is this expected behavior.
I'm unaware of any known issue that would result in clipped layers not drawing in the layout (as expected), but drawing in the printed map or the exported file.
There may be something specific about your map, layout rendering, export options, etc... that results in the clip being ignored. Can you contact Esri Support? They are better equipped to handle troubleshooting steps and gather bug data. They can be contacted at https://support.esri.com/en/contact-tech-support.
When I export from map or layout, the clipping remains. You'll need more details that are specific to your workflow (exact steps to reproduce), which you'll need if this goes to tech support (likely outcome). In addition, what kind of video card are you running? Is that a vector tile layer that is being clipped?
Life is to short for ESRI tech support, my issue seems to be linked to the fact that the map was using old enterprise geo-databases (for some of the layers) which have yet to be upgraded two fixes came to mind duplicate the data out to a current file geodatabase or use donut buffers with a white fill. Went with the second option as I find that having a single source of data is always preferable when you come back to it in a couple of years
Would you be able to provide more details on the old enterprise geodatabases that you felt were the cause of the problem such as GIS version installed (e.g. SDE 10.2, 10.3, etc.) and database type (e.g. SQL Server 2012, Oracle 10g, etc.)?