Find a seat bottle cage frame that holes in the back surface. Then bolt a stem Garmin computer mount there. i.e., a circular Garmin mount that is meant for installing a Garmin computer on top of the bike stem.
I tried lots of things - including zip ties and lots of electrical tape connected to the back of an X-lab turbo - and I landed on using the X-lab super wing. That’s the solid piece rear bottle carrier (the turbo wing is two pieces, one for each side). Yes, I bought the super wing JUST for the ability to mount the darn Radar. The super wing has a solid back with holes in it - and those holes are perfect for mounting a garmin mount. It is really secure and holds the radar at an appropriate angle. That’s what I have done because I am short and I literally have zero room under the rear bottle cages to mount anything. I can’t speak to the new Varia because it has a different mount, but looking at it - it should work just fine too.
I use a top cap Garmin Mount on the back of the bontrager rear cage. It works but is hard to get off.with a cage or 2 mounted. I just leave it on and charge like that.
I have also put it on the seatpost with the rubber mount
I got a Garmin spoon mount. Then drilled extra holes as needed to line up with the water bottle cage holes. Used different length bolts and rubber bushing as necessary. Has worked great. On 1 bike I have lined up vertically. On another I did it horizontally. Clean and works great. I also superglued a camera lens cap strap I hook on the cage so if were to get knocked off still have it.
Barb L