I've found out wat caused these problems.

To summarize it: using VLAN's and creating bridged network interfaces for it in VMWare workstation doesn't permit encrypted traffic (HTPPS, SSH, RDP, ...).

What did I do to track down the problem: boot up older computers with Windows 10 1909 and Workstation 15. -> Everything worked. So I upgraded Windows 10 to 20H2 and VMWare workstation to 16.10 -> Everything still worked.

Then I started thinking: what's the only difference left between those old computers and the new ones???

-> The network adapter, the new ones had onboard RealTek adapters and the old ones had Intel adapters.

I added a PCIe X4 Intel adapter to one of the new computers and disabled the RealTek adapter in the bios.

Everything works perfectly now. So huge warning: watch out with RealTek adapters and VMWare workstation!!!