As previously rumored, today Tamron announced the first mirrorless lens for Nikon Z-mount: Tamron 70-300mm f/4.5-6.3 Di III RXD (model A047). The full press release can be found here.
Tamron has been already working with Nikon and the result was the Nikkor Z 28-75mm f/2.8 lens, which was actually the first Tamron lens for Nikon Z-mount.
I was told that Tamron will not make any mirrorless lenses for Canon RF-mount and if you are wondering why, you can check this post:
Viltrox: “We have been told by Canon to stop selling all RF mount products”
