Vostro 14 5410 connected to Lenovo universal thunderbolt 4 dock - dual 4k@60Hz missing

Hello,

I've got Vostro 14 5410 laptop with Intel i7 processor onboard. That model is equipped with Thunderbolt 4 port. I connected the laptop to a Lenovo Universal Thunderbolt 4 docking station (40B0) which supports up to 4 x 4K@60Hz monitors. I use only two 4K monitors which are compliant with DP 1.2 standard and connected to the dock with DP cables.

Initially the setup was working fine which means both screens was working at 4K@60Hz. But after a BIOS/ Windows /  drivers update screens refresh rate have been degraded to 30Hz only. 

I updated the dock's firmware to the latest version. I reinstalled official drivers from Dell's page to replace the ones updated from Windows Update. Also, I tested restoring BIOS settings to factory and BIOS defaults. But the issue still persists. 

The dock has been successfully tested with another laptops - Lenovo Legion (with Thunderbolt 3) and some modern model of Asus mid-level laptop (I don't remember the model). 

I attempted to open a support case to Dell support but they refuse to diagnose that. My last resort is to obtain some Dell docking station - but it's quite expensive option to diagnose :). I'm really disappointed and the most probably that's my last Dell device. But right now I'm not considering replacement of the current one. 

It would be great if somebody could know how to troubleshoot that and restore dual 4K@60Hz mode.