xen ovmf/uefi firmware does not save screen resolution

["mhbeyle@xxxxxxxx" <mhbeyle@xxxxxxxx>]

    Hello Xen users ...
        
        I have a problem with a hvm domU that uses ovmf/uefi firmware
        ans loads a windows 10 SO.
        
        When windows loads, screen resolution is always 800x600 mode and
        there is no possibility of switching to another one.
        So I change resolution into UEFI bios (Tiano Core), save and
        restart with no change. Screen resolution is always the same, on
        boot loading and windows.
        
        I have tried changing several settings in the configuration file
        (vga, videoram) with no results.
        
        Screen resolution can be changed in Legacy BIOS mode.
        
        
        Any idea what I need to look at? I am completely lost with this
        issue ..
        
        Dom0 is running under Debian (5.10.0-17-amd64) and xen version
        is 4.14.5 (xen-3.0-x86_64).
        
        Thank you very much in advance and best regards.
        
        ------------------
        MhBeyle ___