My guess is aggressive compilation of content in the project’s folders, even when that content is not in any map (possibly due to some kind of bug). Which can be an issue every time the editor (rightfully) decides all the shaders (in the project) need to be recompiled.
If I understand correctly, the engine can be reconfigured to use ODSC instead.
To do it for all projects, I added to the [SystemSettings] section of
C:\Program Files\Epic Games\UE_5.0\Engine\Config\Windows\WindowsEngine.ini:
[SystemSettings]
...
;Activate ODSC for all projects
r.ShaderCompiler.JobCacheDDC=1
Now after creating a new project with starter content, only 150 or so shaders get compiled! \O/
And if I put the JobCacheDDC=0 and reopen that project, sure enough a cr*p-ton of shaders get queued for compilation again.