I have a big problem with the stem of my TT023.
It doesn't hold properly, so the basebar twists when there is a strong shock. For example, I have just ridden through a pothole and the basebar has twisted a little in the stem.

As a result, I can no longer brake as the brake cables are crushed.

I have already used carbon assembly paste and tightened all the screws evenly.

Any ideas or other experiences?

I have routed the brake lines from the brake levers to the brake bodies. I also tightened the stem at the bottom front first.

I had similar issues: the stem would spin on the steerer, and the handlebar would spin in the stem.
I ended up using WELDTITE paste, degreasing the bolts and seat threads, and tightening the bolts to 5.1 Nm crisscross on the handlebars and 5 Nm on the steerer. I contacted the manufacturer and they recommended tightening the bolts to 5.0 Nm-5.58 Nm. I constantly checked the bolts for tightness and tightened them to the target torque. So far, everything is stable.
I would recommend that you first contact the manufacturer with a request and follow their instructions.

Can you post photos of how you routed the hydraulic brake cables? My set of riderever triva brakes is still on its way from Japan and I am currently using cable-actuated brakes. And it is not a good experience so far. I have changed the cables twice and the braking power is still not satisfactory. I have routed the brake cables through the top holes of the stem and brought them inside the stock base bar holes on the lower side. It looks ugly and not so aerodynamic. These cable-actuated cables seem to be so hard to bend and go through the stem as hidden/internal routed cables. I am running 1x sram force with wireless blips so the only cables I have are the brake cables.

This is two brakes mecanical cables and one rear derauler mecanical cable.

Hi Riders!
I bought and assembled VB-023-TT with standard cockpit. And I have a problem: the stem don't fixed cockpit properly.
Have anybody same problem? What torque you applied to stem bolts?

Can anyone measure the horizontal and vertical diameter of the handlebars against the stem?
I suspect that my handlebars are too small - 31.6mm vertical and 31.3mm horizontal. That's why the stem doesn't grip them properly.

https://geometrygeeks.bike/compare/velobuild-vb-tt-023-2023-l,velobuild-vb-tt-023-2023-m,trek-speed-concept-slr-7-2023-l,trek-speed-concept-slr-7-2023-m/

https://www.trekbikes.com/us/en_US/bikes/road-bikes/triathlon-bikes/speed-concept/c/B231/