Hi Pilou,

>> Does not possible to have the same when Split (4 views) is enabled ? <<

The 3D projection, whether perspective or parallel will persist in Split view.
You only need jump to 3D view, toggle projections & jump back to Split view to change between them.

.>> or on the 3D letters up left corner of the "little screen" <<

Yes, it would be appropriate to label "Perspective" / "Parallel Projection" there, in top left corner.

Good thinking
James