Yes, but the performance will suck unless you get KVM working.

Depends on how real you want your Android to be, but Google Android emulator images and Androidx86 exist. Many of these apps run fine in Waydroid as well. A remote desktop UI on a Linux server/VM may be all you need.

If you have decent soldering skills, there are guides online about how you can replace the battery in devices like these by soldering a resistor and a buck converter to the battery pins so it can run permanently without turning the battery into a lithium bomb. If you set up ADB access you can control the screen remotely using scrcpy, all you'd really need is a cheap second hand phone, 20 bucks worth of parts, and a steady hand.

Cheap, commodity Android box as found on eBay, AliExpress, etc.?

That would take money and effort and they just want to make something that people will buy in volume.

It's a device running Android on a bottom-of-the-range SoC with, according to the description, 5 out of "9" gigabytes of "RAM" running from swap space on the internal storage.

Perhaps Doogee could've ported Android better, but I don't think Android will ever run smoothly on this device.

Android contains a lot of tricks to cache as much as possible in RAM so things like sleep/wakeup and app launching can be very fast. You can see the device take a while to launch a terminal on Debian, that's exactly the kind of thing Android uses all of its RAM for to prevent.

Yes, workstation is a bit exaggerated. But it is still more useful to me than stock Android on this hardware.

If it can't run video games, it's a workstation.

80 euro equivalent seems to provide a 2014 Mac Mini with 4GiB of RAM and half a TB of storage over here. Doesn't come with a touch screen, though, and carrying around a PSU for the thing is also a massive pain. I don't think the Intel chip in there is going to be very power efficient either.

M1s? Really?