I had one of these, my first. He's 4 now...
Milestones for us were finally getting the alfamino and omeprazole, after which we followed a program for the milk aversion. He finally stopped vomiting and being furious at the thought of milk. We were also prescribed a weight gain milk to add to the alfamino, which come in flavours - maybe something to ask about. We also had solids aversion. He started eating at nursery at 1.5 years old, and nearer 2 at home. He would only eat when distracted. We're now seeking an ARFID diagnosis because he says he doesn't get hungry and has a very small number of safe foods.
So another milestone was moving to barista oat milk, with vanilla paediasure. We'd worked most of the way up the dairy ladder (he still can't tolerate cow milk) so this helped. This obviously tastes much better than the alfamino! But he still drinks huge amounts of it at bedtime and overnight. But it's keeping his weight stable at least.
My tips for solids, as advised by all the paediatricians and dieticians etc, are grazing trays. Leave little plates of finger foods laying around for him to explore by himself, zero pressure. Let him see you eating the same foods in the same environment. We still do this now.
You sound like you're coping better than I did, I felt like I was going mad the entire time. It's so tough, and lonely. People have no idea what it's like if they've not experienced it, and you get the super helpful comments about how babies won't starve themselves... Health professionals were not super helpful for us, although I get more credibility now with them since having my second baby, who eats and drinks just fine.
When I detail his life with us now, most people are horrified that I'm still dealing with night wakes, milk, food refusal and weight worries. But for me, it's like our normal. He's pretty happy, we're all getting much more sleep now it's just a quick 30 second wake for him to down 300ml of milk and then sleep again. Plus obviously potty trips with that much overnight milk. But compared to how it was, this is manageable. I'm not losing my mind anymore, and I get enough sleep to work full time and just about function! We continue to seek help and support him, but he's stable, extremely active and very bright.
Good luck!!!