FPS drop in windowed fullscreen, window focus vs. unfocussed

I have encountered a wierd fenomena when playing the game in windowed fullscreen.
When the game window is out of focus, say having windows task manager float in
front of it, I get a solid 100-120 FPS from the in game fps counter.
But when i focus the window ei. click on it, it drops to 20-40 fps.

When the window is out of focus I can even see stuff like aura effects and the lightning from the crafting bench running much smoother.

I have noticed that when the game is unfocussed it utilizes 100% of my dedicated GPU and Desktop Window Manager (DWM.exe) uses ~40% of my integrated GPU.
When the game is in focus however dedicated GPU drops to 48% and the integrated GPU rises to 100%. DWM.exe using 90% of my integrated GPU.
So it seems like my dedicated GPU is capable but DWM some how bootlenecks it, when the game is in focus.

On a side note when playing in true fullscreen fps is 90-100. Which is nice but I would like be able to play in window mode for easier web access.

Any suggestions are appriciated

DxDiag: https://pastebin.com/pJuG5xvv

I suggest, disabling your integrated GPU in your system's BIOs. Generally, you don't want both running.

Thank you for your reply.

I have attempted this, but my bios only has the options: "Switchable graphics" and "UMA graphics"(integrated). No dedicated only option.

According to the DxDiag my dedicated card is a "Render-only Device", which I guess means it cant run stuff like explorer.exe or DWM.exe.

Card name: NVIDIA GeForce GTX 860M
Manufacturer: NVIDIA
Chip type: GeForce GTX 860M
DAC type: Integrated RAMDAC
Device Type: Render-Only Device

Thanks for the suggestion though :)

I'd say try the Display Driver Uninstaller and delete anything related to drivers (it defaults to normal windows drivers and doesn't let them update), then download the correct driver for your Nvidia card and disable your integrated GPU under Device Manager.

Unfortunately I dont believe completely disabling the integrated GPU is an option since I'm on a laptop and the screen is conneted through the iGPU.
I will attempt to reinstall the drivers though, it is worth a shot.

I tested on an external monitor, and didn't have the same issue. Had stable 60 fps, but with some dips in resolution due the dynamic res.
Seems like the dynamic resolution doesn't work in windowed fullscreen on my integrated screen, worked fine in windowed fullscreen on the external screen though.

Which Lenovo device is that?

Lenovo Y50-70

I found a fix!
Went to settings -> personalize -> Colors And turned off transparancy effect.
Apparantly this was too much to handle for the integrated gpu while also writing the images provided by the dGPU to the screen.

I also went to This computer -> properties -> perfomance -> settings and ticked adjust for max performance, which has generally made Alt-tab much smoother.

Hope this helps if anyone has a similar problem.
I appoligies if the wording of the settings aren't on point, but my windows is in a foreign langues.

The only thing you can do, is to set the NVIDiA settings to use the High Perfomance GPU and you cannot disable it. Bugger.