Hi Kirill.
Gen2 VMs will be selected by default for SCVMM, Windows Admin Center, and Hyper-V manager when creating a VM. This is because there are many advantages, including the following. Powershell and WMI default has not changed, so scripts that assume Gen1 will not be effected.
- Secure Boot and other security enhancements
- Larger boot device support
- More efficient keyboard/mouse/video, not emulated
We suggest only using Gen1 if the OS in the guest doesn't support Gen2
- Can't boot using UEFI
- OS that requires legacy emulation

Should I create a generation 1 or 2 virtual machine in Hyper-V? | Microsoft Learn