The Steam version of MotD does not include a file "ddraw.dll" which is necessary to start the game. The GOG (Good old Games) version has this file and therefore starts, however you do not need this file from GOG.
Instead, you can use the ddraw.dll from dgVoodoo2.

Download "dgVoodoo 2" from "Dege's stuffs". Unzip the "Latest stable version" (or try one of the older versions). There is a subfolder "dgVoodoo2\MS\x86" with four files:
D3DImm.dll
D3D8.dll
DDraw.dll
D3D9.dll
Copy all four files into the folder
"...steamapps\common\The Mystery of the Druids"

Now you can start and play thhe game. However, it is just in 640x480:

In the folder where dgVoodoo2 is unzipped, there is a program "dgVoodooCpl.exe". Start it. First, you must add the folder where MotD is installed and where now the four new dll files are located.
For all settings now, be sure that this MotD folder is always selected.

The default tab is "General". Switch to the tab "DirectX". Here you can choose several settings depending on your taste or your PC. We want 4K, so in Resolution, we choose 3840x2160. On the "General" tab, I have actived "Enumerate refresh rates", so there is also added "120 Hz".


Now, a look on the 4K screen:


A pity: Instead of the original 4:3 ratio, the screen is stretched to 16:9
In the MotD folder, a new file "dgVoodoo.conf" has been added by using the dgVoodooCpl.exe, the config file of dgVoodoo for that specific game. It`s an ASCII text file. Open it with any text editor (e. g. Windows Notepad).

The dgVoodoo.conf shows what can be changed, and there are several helpful explanations integrated. Important are the settings:
[General]
ScalingMode = centered_ar
[DirectX]
VideoCard = internal3D
VRAM = 4096
Resolution = h:2880, v:2160

2880 x 2160 is 4K with 4:3 ratio. You can change the line according to your monitor / preferences. Here some other examples of 4:3 resolutions:
1024 x 768
1600 x 1200
1920 x 1440
2048 x 1536
2560 x 1920
4096 x 3072
5120 x 3840
6144 x 4608
8192 x 6144

Anyway: Here a screenshot of 4K / 2160p:

The game should work dgvoodoo and even in 2160p.
However two problems might occur:
1. Crashing when saving.
If you save a game, a new window is opened in Windows - and not in the game itself. This call can lead to a crash, but so far I have not experienced that. I other words: You can play and save your progress.
2. Freezing when exiting.
That occurs quite often, regardless the settings. The reason might be the autosave feature that cannot be disabled. You have to end the program using Windows taskbar - end task.

Final words: The technical state of the game as it is distributed here on Steam makes you wonder what is going on here. And what I have seen from the gameplay, I definitely do not recommend the game - regardless its technical state.
Nevertheless, as the game and especially its technical issues are discussed here on Steam, the general topic of this guide, "4K / 2160p resolution and 4:3 ratio", might be found useful.