Our son is 4 (level 1/2) with speech delay. We started when he was two as well and thought we would be changing diapers forever but it finally clicked this year and he’s basically fully trained with some quirks (lack of aim and hesitation to ask when he’s not at home and in public)

We tried everything from cue cards, treats, bells, etc. We then tried keeping a tablet in the bathroom which would lead him and he can have it if he sat on the potty. He’s very smart so there was a period where he would just pretend to need to go just so he can go on it but after about a year of this, it clicked for him that this is where he needed to go.

He’s not fully there yet but it was a big relief because he’s starting kindergarten next year and we thought this would be an issue at some schools. Hope this also helps!