It is possible for a Mac notebook to need more power than the power adapter can supply. The battery is used to make up the difference. Typically this would only happen for short bursts so isn't particularly noticeable, but if there is a persistent heavy load, this could lead to the battery draining even though the power adapter is connected.
This leads to the theory that running Docker inside the Windows 10 VM is causing a huge power drain, probably because the CPU is working hard with many cores active (the GPU might be involved as well). Activity Monitor should be sufficient to confirm the pattern. System Information shows battery current in or out (output is negative) and voltage.
If you want more detail, there are tools which can report power consumption of various parts of the computer, e.g. iStat Menus, which can show even more detail about the CPU if you also have Intel Power Gadget installed.
I've had this happen recently when doing long video encodes. In my case I discovered that running the power through the HDMI multiport adapter reduced the current below the recharge threshold.
Other things that can cause it are using third-party power supplies, or a 60w supply on an 85w machine.
Yah I get this when I plug into my USB-C/Thunderbolt Display, without Fusion.
It is 'sort of enough' if I'm not doing much to not drain the battery, but if I start doing heavy stuff (like compiling a bunch of code over and over again because I keep screwing stuff up innovating), the battery drains even tho it says it's 'charging'. I have to plug in a regular 85w adapter otherwise it will trickle down to 0.
Ah, brilliant! I've never seen this behaviour before, but what you say re: passing power through an external hub/adapter not delivering full power makes perfect sense. And it so happens that I am using an external HDMI/USB hub with power pass-through.
It is still interesting / unexpected that VMWare Fusion running Windows 10 with a nested hypervisor (Docker) results in so much power draw when everything is effectively 'idle' i.e.: the nested Docker Desktop failed to launch correctly, and the Windows 10 VM in which it resides isn't running any applications.