DD was a little bit similar. She hit all milestones for number of words, so I wasn't worried - but then other people pointed out she never asked for anything. She was a late waver, and would point at things in books if asked (e.g. "where is the cat?") but not to get our attention or point something out to us until much later.
She did come to share things with us though - I can't really remember what and at what age.
This waiting bit is hard, but generally I think it's hard to get an ASC diagnosis much before 3, and ADHD generally later (more like 7). The do often go together (and there are some overlaps - e.g. executive function issues and hyperfocus are common to both).
Generally the advice is to try to get involved in whatever they are interested in (even if it seems a bit odd, and even if they don't show any appreciation for that to start with). Try to find ways to make yourself useful to what they are already interested in/doing.
Here are a couple of videos that may be a useful starting point by a YouTube channel I really like. She also has a FaceBook group (same name) and there are lots of parents there who are worried but don't have any diagnosis yet, so it's a good place to share worries and ideas.
Interaction/play ideas:
Eye contact:
Other ideas (not therapy):
But the whole channel is great I think: www.youtube.com/c/NurturingNeurodiversity/videos
Chirp Speech Therapy also has a bunch of videos with ideas on sensory stuff, eating, clothes, and interactions as well as specifically speech. Worth an explore: I found some useful ideas here when DD was small:
www.youtube.com/user/ChirpSpecialNeeds