Your thru-axle is indeed 12mm with a 1.75 thread pitch based on the photo you provided.
I am familiar with the Kinetic Traxle adapter for their trainers, and for that it would take the Traxle Coarse T-2101 to match up with your bike/thru-axle.
A specific note regarding using this product on a non-Kinetic trainer is to ensure that your trainer can accommodate the width of the Traxle. In your case, this adapter is 205mm long, so that is the critical dimension for fitting it to your Tacx trainer.
Link to KurtKinetic Traxle info
Garmin does have a FAQ on which thru-axle will fit your bike. Based on information there and what your information offers, it appears that a Tacx/Garmin model T1708 E-Thru is the one you would need.
Which Tacx Thru-Axle Will Fit My Bike?
Here is a screen grab from that FAQ page:
These two should give you a couple of options (assuming the Tacx Boost trainer is wide enough for the Kinetic axle) in case you have trouble locating one or the other. I would probably veer towards the Tacx/Garmin model in case the profile of the axle ends are not consistent between brands.