The lugs you have pictured that Metier Velo LLC uses are actually 3D printed titanium. He is somewhat local to me and we spoke several years ago, 2017 maybe? Anyway, a very basic description of the process used to make those lugs is that they take a pile of titanium powder and blast it with a high powered laser to melt it together in whatever shape is desired. At the time, he told me only two manufacturers in the USA were using this process, one was in Illinois and I can't remember the location of the other.
Don't know if the process works with steel, but it sounds high tech and probably spendy. His bikes weren't cheap, but they looked super cool. I know that wasn't super helpful information, but that's what I was told about those lugs, according the the guy that had them made.
I know almost nothing about this process, but I would think blasting powder with a laser would produce a product with a high level of porosity and voids.
https://www.xn--mtier-vlo-b4ag.com/bicycles1.html
I just checked his website. Looks like there is an email, so you can contact him and ask him about it. Looks like like he moved to New Mexico. He used to be just outside of Salt Lake City.