Connecting HP monitor to MacBook Pro.

<<. the yellow start page for Ventura but nothing else. >>

you get a clear stable picture of the Ventura wallpaper, at an expected size that fills the display?

Then your display is working as designed, and you need to understand that so that you can bend it to your will.

the default setting for a second display is "extended desktop". The screen area of built-in and the external displays are concatenated along an edge (which you can specify) and the mouse moves freely across the boundary between Virtual displays. The mouse can drag a window all the way or part way across the boundary, and that window will continue to scroll "the right way".

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The mirror display screen that used to be shown is this one:

the two boxes representing the screen area are ALMOST co-incident, leaving just enough difference to drag them apart if desired.

Both displays are set to a computed 'compromise' resolution that both seem able to attain, and both are run With ONE display generator, is exact sync with each other.

There are more than a hundred computers issued since 2006 that carry the name MacBook Pro. Which is yours, by year and display size, and if 2020, processor type?

There are many different versions of MacOS that you could be running. which is yours?

There are dozens of HP display you could be connecting. What model?

There are several cabling ways you could be attempting this connection. EXACTLY what cables, adapters, and docks are you using? please mention every item.