Possibly due to C++20, there are now documented flags that force posix-compliant behavior on Windows when deleting a file. It is not documented when this was added to the Windows kernel. (It is also possible the behavior of DeleteFile and/or DeleteFileEx has changed according to random user comments on the internet, although the documentation for those functions still claim not to provide posix-behavior here.) But while browsing the documentation site, I discovered it is now possible to request posix-compatible deletion semantics via:

https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/ns-ntddk-_file_disposition_information_ex

We can infer some of the dates where this is first available from the comments on the official C++20 STL implementation (apache-2 license), such as microsoft/STL#1559

1809 | Redstone 5 | October 2018 Update (added FILE_DISPOSITION_FLAG_IGNORE_READONLY_ATTRIBUTE)
1607 | Redstone | Anniversary Update (added FILE_DISPOSITION_FLAG_POSIX_SEMANTICS)

It is then possible to detect the error if these functions/types are not available at runtime for the filesystem or operating system, and fallback to the current code.