Delay in social communication skills - how can I help my 2.6 year old?

[needhopeandluck]

My son is 2.6 and is visibly behind with his social communication skills (rarely waves bye, does not say hello, does not look people in the eyes when they speak to him)...
SALT diagnosed him with severe receptive language delay. He never answered when we called his name and at 2 he could not understand pretty much any instruction. Now he can understand a bit more but very far behind his peers, my guess is that he is at the level of a 18 month old, so a 1 year behind.
Paediatrician said he has a delay in social communication skills....not sure if it is a delay or disorder...it was an observation she made in the meeting not a diagnostic. I guess they want to wait until he is at least 3 before doing an assessment.
He can say a lot of words now (he started pointing at 2 and it all started then; actually he used to point at 13 months and at some point he stopped) but he did not figure out yet that he can use words to ask for things.
With regards to pointing, he uses it to show us things and rarely to ask for things. He mainly hand leads us to what he wants.
He was waving bye and shaking head no at 14 months then stopped, so he had a regression, which I understand it is something very concerning.
He learned to say and wave goodbye again at 2 after he started pointing again, did it for a while then he stopped again. Sometimes he did it out of context...
I spend a few hours a day with him at home trying to help him with his speech and he is making progress, literally adding words every week and even stringing 2 words together sometimes.
Looking to get SALT help too for professional support.

Nursery has been useless so far, SENCO still to advise on things and my expectations are low in terms of support he can get in the nursery setting.

What can I do to help him with his social communications skills?
Has anyone experienced this and tried certain things that worked well?

@needhopeandluck Hi, how's your son doing?

@Dadofboy842 My son will be four soon. He has made a lot of progress with his understanding (he can now follow one step instructions) and speech (can say sentences, ask some questions; although he is not yet fully conversational). He has an incredible memory (he can memorise books) and can grasp more conceptual things effortlessly (e.g. 3D shapes like cone and cylinder), but he is not yet interested in playing with other children or interested in interacting with adults he is not very familiar with in general. He plays alongside them and is better at sharing and can take turns with adult support, but he is significantly behind his peers in terms of playing together.

@needhopeandluck Thanks for answer. Sorry for ask but does he has some diagnose?

@Dadofboy842 No diagnosis. He has been referred for an ASD assessment however, so we are waiting for that. I am quite certain that he is neurodivergent as his development is not typical.

@needhopeandluck Hello, some update after almost a year?

@Dadofboy842 He is definitely making progress. He can talk in sentences, although not conversational yet, he can ask for what he wants, he can answer some simple questions (not things like 'How was your day?'), can be clear about what he wants to do and where he wants to go. His play has evolved as well, we now work on our scrapbook together, he is building with lego and enjoys colouring (although it is quite immature for his age). He makes up his own songs and can follow instructions. He is still behind with his receptive language and pre-writing skills. What made the most difference for us was the development of his receptive language, which means he can now understand when we tell him where we are going (so he gets a chance to say no) or what we are going to do, can follow instructions. We have delayed school start which I think was the right decision for us.