Made some additional quality of life and - obviously - weight saving adjustments which all relate to the original frame accessories supplied by BXT.
Keep in mind that some of these changes might compromise your ride experience and could also lead to safety concerns especially for heavier riders. In case of the exact products I've installed, I did not experience any alarming sign of instability, cracks or excessive flexing (At a rider's weight below 75kg with some peak sprints over 1000W or 1-minute intervals at 400-500W riding out of the saddle done as testing within the last ~1000km)

In order to sum up the potential weight saving probabilities I listed the original+new weight of the following components:
- 15g: BXT frame to handlebar top cap 25g swapped for a 9,5g 3d printed (probably carbon fiber reinforced nylon) version delivered with the imtos bike integrated handlebar
- 31g: BXT expander plug 38g swapped for a small 7g version
- 52g: BXT thru axles 86g (M12*P1.5mm, TL 17mm, 119,5mm front, 163,5mm rear) swapped for 34g lightweight AL-7075 axles 117mm front, 161mm rear (which due to the shorter length only screw in for 3-4 revolutions compared to about 5-6 revs on the or. ones - which for me personally is not concerning since the actual load is on the frame dropouts and the hub cups themselves, not the thru axle holding the hub in place. Just keep in mind to not overtighten them and always use a torque wrench/be careful screwing them in when fixing a flat tire on a rideout)
- 64g: BXT seat post 189g (only carbon part) with BXT saddle clamp 68g (metal parts) modified to fit a lighter more flexible clamping system which included cutting the top part of the or. seat post and drilling/milling out some holes for the new bolts/screws with a weight of 156g (carbon part) and 37g (metal parts) I mainly modified this because I really disliked the inflexibility of the original clamping system in terms of adjustment options. I had to tighten it well above 10 nm to avoid the saddle tilting front- or backwards when either applying power in a seated position or when sitting upright to take a drink. To readjust the angle it wasn't enough to just losen the bolt - no! The metal parts always wedged themselves into the carbon part of the seat post and in most cases I had to use a hammer to unstuck the saddle clamp. Slightly adjusting the saddle angle or the offset was equally hard since the same issue occurred. With this new system I can freely adjust the saddle angle or offset with two separate bolts and have not had any problems with any unwanted movement so far. Before cutting/drilling in the carbon part I was slightly concerned about creating a structural weak point when removing material. But since the seat post is manufactured in a pretty chunky way, there is more than enough material left to withstand the significantly lower forces with my new setup. I only need to tighten the bolts to 5-6 nm each to get a perfectly secure fit.

Overall I'm now down to 6.8 kg (no pedals, cages, light/GPS mounts but including the spindle powermeter) or 7,45 kg with everything mounted (even radar light, bike computer, speed sensor and aero bottles included)

Build my size M BXT 145 frame in glossy transparent blue with Ltwoo eRx, XMCarbonspeed aero 50/60mm wheels on 30mm tyres and managed to get the system weight down to 7,524 kg including everything mounted on the bike.
Without pedals, bottle cages, sensors or rear light (usually advertised when selling fully build bikes) its at 7,05 kg.

The build is still in a somewhat affordable range of about 3200 € total.
Pairing up the quite heavy weight of this particular frame with my choice of components is probably not the best idea when going for a lightweight build. But hey, the bike looks dope, drives nicely and is still pretty light.

An alternative for this frame would probably be the Spcycle R065 - with similar geometry (R065 has a slightly longer wheelbase) but about 250g lighter for the frameset.

In my case the BB area is slightly rubbing on the P505/P515 powermeter even with 2mm spacers applied... so keep that in mind when going for magene powermeters.

I had some issues with the seatpost slipping on the first rides. But after thoroughly cleaning the seat post itself, the clamp and the inside of the seat tube - so every contact surface upon torquing it up - that issue is fixed.
Been riding for about 3000 km now and there is nothing to complain about.