What is the difference between this an "saya ada di sini"
I think there's is almost no difference at all. As you may have known, Indonesian is very lax with the verb "be".
If you eliminate it, usually it doesnt change the meaning at all.
All Might said
Is there a difference between ''saya di sini'' and ''saya ada (di) sini''?
There's no difference me think
The 'di' shouldn't be omitted because it's a location marker. The difference is just that having 'ada' there is more formal.
What does di mean?
Di is more like 'At' in English for me
It can mean in, on, or at, as U have seen the examples given by the app