@uk_dave Concerning the Thunderbolt Docks, we exclusively use the HP Zbooks with the HP Thunderbolt 3 docks and they always utilize the discreet graphics (Nvidia Quadro in our case) when running Solid Edge.
Maybe HP has wired the Z-books differently but the Dells do not use discrete when docked to Thunderbolt. Apparently this all has to do with how the GPUs are internally wired/connected.
Do you have the monitors connected to the Thunderbolt docking station or the laptop directly? With the Dell if I connect the monitors to the Thunderbolt I will get Intel graphics while docked. If I connect the monitors directly to the laptop but then dock the rest of the devices to Thunderbolt I get Nvidia graphics.
Are you running a Thunderbolt docking station with an external Nvidia GPU built in?
The interwebz is littered with people asking about not having their discrete graphics working while the monitors are plugged in to the Thunderbolt docking station and the laptop connected to the Thunderbolt.
If you are able to successfully accomplish this you are doing better than everyone else I know of running Thunderbolt and monitors connected directly to Thunderbolt.
I don't have Thunderbolt dock. My laptop uses HP UltraSlim Dock D9Y32AA. I've used it with and without a dock and there's no notable differences on performance.
@jylik Sounds like you are using the Zbook 14u/15u G3 model which is different than the Zbook 15/17 models that cannot use the ultraslim dock and must use the TB 3 Dock. I think the "u" models are based on the Elitebooks and thus may be running that BIOS which is why you don't have the same options. Unfortunately I don't have much experience with those other than to know you are stuck with the Radeon Pro GPU and cannot get them with the NVIDIA Quadro GPUs.
My only suggestion would be to insure that the Radeon Pro driver is up to date and to insure that it is set up correctly. It may have settings to specify what apps run on what graphics. I am just not knowledgeable about the driver settings for AMD products.
@KennyG Yes, my bad. It's indeed Zbook 15u G3. Radeon drivers are up to date and there's not much options on software. I can set SE to "high performance" profile from Radeon settings but it still uses both integrated and discrete GPUs.
Maybe there's not much to do. All the googling just indicates that full discrete mode is possible with Nvidia, but no mentions with AMD products.
@uk_dave From what I understand, the GPU's DisplayPort bus must be mutliplexed to the ThunderBolt bus in order for the GPU to output DisplayPort on the dock, which apparently HP does with the Zbook 15/17 and probably a couple other Zbook models.
I will say that the TB3 Dock is a pain in that it requires about half a dozen drivers/firmwares to be installed on it to even work compared to other dedicated connector type docks that did not require any. You also need a couple on the PC itself to insure the TB controller passes the info to the dock correctly. The HP gen 1 TB3 dock even required an active DipslayPort connection when installing the DisplayPort drivers opr else the DiaplyPorts would not work. The gen 2 dock no longer requires that.