Send and Delete

If you find no other tool for this, I feel like you could (ab)use the “Trash Can Versioning” in syncthing.

Deletion on the originating device would need to be done manually after making sure the file is on the target device.

If you want to have more than one target device, I guess you could somehow share the trashcan folder itself…

Also, the solution people seem to envision here could easily be done if someone were to implement some form of this suggestion:

Which is a far more general approach and is more likely to get support from from the main devs, and indeed has been discussed on github