Update on my slipping plug. I cleaned everything with alcohol and torqued it to 10nm. It's not slipping anymore. Well in place

However, I am getting a clunking noise from the hamdlebar from when I ride. It clunks when I go over bumps or when I sprint and rock the bar a bit more. I have disassembled everything many times, torqued the top bolt many times and also torqued the stem bolts to recommended 5NM.

When I rétorque everything, the sound goes away but quickly comes back, like if something loosens up, but there is no play that I can feel in the headset.

I am running out of ideas of what can cause the clunking noise. Any idea is more than welcome. I am getting crazy with that sound when riding.

LTwoo hydraulic calipers are flat mount brakes that need to use their own adapters, regardless of appearance. It's LTwoo's way of getting around Shimano brake mount patents. Your best bet is to use either regular post or flat mount calipers with appropriate adapter. I believe ZRace provides IS adapters for either caliper style.

replacement bolt for the rear shock mount would be $25.

You can buy any bolt and cut it to the size you need. Its the 5 minutes of work. I've replaced mine already.

Here's I think where I am (I'm considering a size 54 in all of these frames)

Velobuild 268  more aggressive
Lightcarbon LCR 017  similar but slightly longer stack (7mm, so marginal)
TanTan X38  longest stack by 20mm over the Velobuild 268

I feel like any of these options above would be a great frame to move on from my Triban?

Upon further study I'm thinking:
Velobuild vb-r-268
sp-cycle sp-R065 

I guess it would be pretty straightforward to create a questionnaire that would fill in a simple database with important metrics. Without knowing your age, weight, measurements, flexibility and so on, we're shooting in the dark, as you didn't write much in way of context.
The Triban RC520 is pretty crap, it's not just in your head.
Assuming you're young enough, either flexible or willing to get flexible enough (not that hard), i dont think you need to overthink it too much, the VB 268 will probably be life changing, and you dont need to spend more, especially if you order it black. To customize, you can get decals cut locally (or via aliexpress) for cheap, it's a good way to save 100 usd.
Given your budget, you should assume you'll be your own mechanic going fwd, because labour cost post inflation & now that bikes are fully integrated can double the cost of the bike in a few visits to the LBS... You'll also learn a ton.
Expect to start with all the spacers on the 268, because that decathlon bike has a VERY relaxed geometry. Then you may find yourself removing spacers over time, which will mechanically go faster on the flat. From this perspective, make sure to buy a cockpit that allows to have spacers above the stem, otherwise you'd have to cut the steerer every time, which is a disaster. It would also be pretty smart to get a bar & stem vs cockpit, because you may also want to change stems.
From a bike fit standpoint, given the uncertainty, you would benefit from a bike that is NOT fully integrated, to allow making changes more easily.
Changing anything on a fully integrated bike is absolutely miserable.
The best bike is a comfortable one that fits you.

Thanks for the critical feedback. I should have known better to include more details on "myself". Regarding the Triban I have drop down a spacer or two since I purchased the bike and I am conscious of trying to ride in the drops as much as possible.
33M, very flexible, 75kg/165lb, 5'8", inseam  31".

The thing I am MOST excited about is building this bike out myself. I've done all the mechanics on my current Triban and my old Fixie bike, including the upgrades listed in the OP. I'm not at all concerned about building this one out, except for the integrated wiring and integrated cockpit. The integrated cockpit sounds the most frustrating if I need to change things.
Definitely wanting to keep this build far under 2k, we will see how close I get, but I need to start from a specific frame and build things out from there.