Sorry, I'm not the creator, but from watching his last video, the main feedback he would like to have is related to what would be the ideal distance of the axle needed to pretension the bearings of the hub, so it allows them to rotate freely and without any jiggling

The best success he had was using an axle that is 0.1mm shorter to tension the bearings. There are some schematics on the following video and more details around 8:00 mark:

"I Built 10 Tilting Trikes So You Don’t Have To"

As mentioned by @matchanik, there could also be mechanical improvements, both in terms of strength and ease of manufacturing, like the connection between the axle and the steering block.

It's possible that those two aluminum pieces, joined by a bolt, will fail in the short term. You have a high concentration of stress on the compression side, while the piece tries to separate on the tension side. It would be good to consider some way to manufacture that part as a single piece, or to pass the axle through and secure it along its entire circumference. Perhaps examining the actual Lefty fork could give you some ideas.