OK I have started to test it now.

My cernel is now:
$ uname -a
Linux DEM-RSZABO-U20 5.7.0-050700rc7-generic #202005242331 SMP Sun May 24 23:33:19 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

with self compiled and patched nvida driver (the latest driver kernel module with the mainline kernel does not compile without a patch see (https://gitlab.com/snippets/1965550) ):

So Now I run Nvidia driver and external monitor over the thunderbolt 3 where also the FireWire interface is running. 
Nvidia 
$ nvidia-smi -a

==============NVSMI LOG==============

Timestamp                           : Wed May 27 19:57:17 2020
Driver Version                      : 440.82
CUDA Version                        : 10.2

Attached GPUs                       : 1
GPU 00000000:01:00.0
    Product Name                    : Quadro T2000
    Product Brand                   : Quadro
    Display Mode                    : Enabled
    Display Active                  : Enabled
    Persistence Mode                : Disabled
    Accounting Mode                 : Disabled
    Accounting Mode Buffer Size     : 4000
    Driver Model
        Current                     : N/A
        Pending                     : N/A
    Serial Number                   : N/A
    GPU UUID                        : GPU-e970a3f0-ccb4-aca2-c0bb-c63d35d10fdc
    Minor Number                    : 0
    VBIOS Version                   : 90.17.1A.00.A3
    MultiGPU Board                  : No
    Board ID                        : 0x100
    GPU Part Number                 : N/A
    Inforom Version
        Image Version               : G001.0000.02.04
        OEM Object                  : 1.1
        ECC Object                  : N/A
        Power Management Object     : N/A
    GPU Operation Mode
        Current                     : N/A
        Pending                     : N/A
    GPU Virtualization Mode
        Virtualization Mode         : None
        Host VGPU Mode              : N/A
    IBMNPU
        Relaxed Ordering Mode       : N/A
    PCI
        Bus                         : 0x01
        Device                      : 0x00
        Domain                      : 0x0000
        Device Id                   : 0x1FB810DE
        Bus Id                      : 00000000:01:00.0
        Sub System Id               : 0x09261028
        GPU Link Info
            PCIe Generation
                Max                 : 3
                Current             : 1
            Link Width
                Max                 : 16x
                Current             : 16x
        Bridge Chip
            Type                    : N/A
            Firmware                : N/A
        Replays Since Reset         : 0
        Replay Number Rollovers     : 0
        Tx Throughput               : 1000 KB/s
        Rx Throughput               : 6000 KB/s
    Fan Speed                       : N/A
    Performance State               : P8
    Clocks Throttle Reasons
        Idle                        : Active
        Applications Clocks Setting : Not Active
        SW Power Cap                : Not Active
        HW Slowdown                 : Not Active
            HW Thermal Slowdown     : Not Active
            HW Power Brake Slowdown : Not Active
        Sync Boost                  : Not Active
        SW Thermal Slowdown         : Not Active
        Display Clock Setting       : Not Active
    FB Memory Usage
        Total                       : 3911 MiB
        Used                        : 976 MiB
        Free                        : 2935 MiB
    BAR1 Memory Usage
        Total                       : 256 MiB
        Used                        : 7 MiB
        Free                        : 249 MiB
    Compute Mode                    : Default
    Utilization
        Gpu                         : 2 %
        Memory                      : 12 %
        Encoder                     : 0 %
        Decoder                     : 0 %
    Encoder Stats
        Active Sessions             : 0
        Average FPS                 : 0
        Average Latency             : 0
    FBC Stats
        Active Sessions             : 0
        Average FPS                 : 0
        Average Latency             : 0
    Ecc Mode
        Current                     : N/A
        Pending                     : N/A
    ECC Errors
        Volatile
            SRAM Correctable        : N/A
            SRAM Uncorrectable      : N/A
            DRAM Correctable        : N/A
            DRAM Uncorrectable      : N/A
        Aggregate
            SRAM Correctable        : N/A
            SRAM Uncorrectable      : N/A
            DRAM Correctable        : N/A
            DRAM Uncorrectable      : N/A
    Retired Pages
        Single Bit ECC              : N/A
        Double Bit ECC              : N/A
        Pending Page Blacklist      : N/A
    Temperature
        GPU Current Temp            : 48 C
        GPU Shutdown Temp           : 98 C
        GPU Slowdown Temp           : 93 C
        GPU Max Operating Temp      : 87 C
        Memory Current Temp         : N/A
        Memory Max Operating Temp   : N/A
    Power Readings
        Power Management            : N/A
        Power Draw                  : 4.12 W
        Power Limit                 : N/A
        Default Power Limit         : N/A
        Enforced Power Limit        : N/A
        Min Power Limit             : N/A
        Max Power Limit             : N/A
    Clocks
        Graphics                    : 300 MHz
        SM                          : 300 MHz
        Memory                      : 405 MHz
        Video                       : 540 MHz
    Applications Clocks
        Graphics                    : 1575 MHz
        Memory                      : 4001 MHz
    Default Applications Clocks
        Graphics                    : 1575 MHz
        Memory                      : 4001 MHz
    Max Clocks
        Graphics                    : 2100 MHz
        SM                          : 2100 MHz
        Memory                      : 4001 MHz
        Video                       : 1950 MHz
    Max Customer Boost Clocks
        Graphics                    : N/A
    Clock Policy
        Auto Boost                  : N/A
        Auto Boost Default          : N/A
    Processes
        Process ID                  : 1489
            Type                    : G
            Name                    : /usr/lib/xorg/Xorg
            Used GPU Memory         : 141 MiB
        Process ID                  : 2236
            Type                    : G
            Name                    : /usr/lib/xorg/Xorg
            Used GPU Memory         : 383 MiB
        Process ID                  : 2447
            Type                    : G
            Name                    : /usr/bin/gnome-shell
            Used GPU Memory         : 221 MiB
        Process ID                  : 2930
            Type                    : G
            Name                    : /usr/share/skypeforlinux/skypeforlinux --type=gpu-process --field-trial-handle=11031610151995791585,8538431210028618818,131072 --disable-features=PictureInPicture,SpareRendererForSitePerProcess --gpu-preferences=KAAAAAAAAAAgAAAgAAAAAAAAYAAAAAAAEAAAAAAAAAAAAAAAAAAAAAgAAAAAAAAA --service-request-channel-token=10971760252379018322
            Used GPU Memory         : 107 MiB
        Process ID                  : 3330
            Type                    : G
            Name                    : /usr/share/teams/teams --type=gpu-process --enable-features=SharedArrayBuffer --disable-features=SpareRendererForSitePerProcess --gpu-preferences=KAAAAAAAAACAAABAAQAAAAAAAAAAAGAAAAAAAAAAAAAIAAAAAAAAAAgAAAAAAAAA --service-request-channel-token=3435244427162261716
            Used GPU Memory         : 108 MiB