Windows 10.
Found a group of two identical files by XXH3 residing on the same disk.
Selected both files in the group.
Pressed the Hardlink button. Proceeded with the confirmation prompt.
The group vanished from the list.
No new messages in the log.
None of the corresponding files in the filesystem gotten replaced by a hardlink. They remain redundant.

I installed and ran this software on a large disk overnight in order to deduplicate files between two big backup archives on it. That wasn't the only group. There's more than I could hardlink manually. This has been a waste.

If hardlinking wasn't implemented on Windows — the readme should've warned me in advance instead of advertizing:

works on Linux, Windows, macOS, FreeBSD and many more