WampServer

I have a test PHP page under C:\Users\erik\OneDrive\test
When trying to create an alias (Apache > Alias directories > Add an alias) for that directory, I get the following:

Enter the destination path of your alias.
...
: C:\Users\erik\OneDrive\test\
This directory doesn't exist.

When creating an alias to a directory outside of OneDrive (e.g. C:\test) and then editing the alias to point to the intended directory, the PHP page displays fine (changed the directory on both line 1 and line 3, not sure if both are needed).

Also tried the same with a 'proper' web app - not just a test page - and that works fine as well

Was this the info you're after?

Unckeck the "on demand" option on the OneDrive Settings then sync required directories and wait to files to be download.