I would have sworn I read that the developer had an agreement with the GIMP team to just put it into GIMP 3 natively.

Was I imagining things?

If you've never heard of it, it's a plugin that adds "Heal Selection" to GIMP that behaves a lot like the same feature in Photoshop. It's a killer feature! It can also "Heal Transparency", and the plug-in itself can be run manually with many more options. It works really well.

Here's the discussion I found about getting it to work in GIMP 3 under Windows: https://discuss.pixls.us/t/need-help-installing-resynthesizer-plug-in-for-gimp-3-0-in-windows-10/49019/2

In short, the files go into your app settings GIMP folder. The exe goes into "plug-ins" inside a sub-folder named the same as the exe (minus the .exe part), so; plug-ins/resynthesize/resynthesize.exe, and the scm files go loose inside scripts. The scripts will appear in GIMP under Filters/Resynthesize.