Can we assume that it is updated constantly when new charging points come Online and the update can be done at home using a laptop or Smartphone and not the dealership?
No, you cant assume (oh that we could!). That depends on the car and system, and I think is different for Map data vs Charger data.
Here is what I know for ours - others will vary!
For map data...
My youngest Corsa E you update via a memory stick from your home computer. The process is a complete PITA, but is at home and free.
The eldest's Renault ZoE seems to do it over the air, but it's a bit hard to tell.
Our Fiat 500e uses TomTom in the navigation. It seems to be updated over the air with no interaction.
The Polestar is live, in that Google maps is constantly being updated. It uses streamed data that is then cached locally, just like on your phone. If you are off line (no signal) it uses the cached data until you are on line again.
For charger data, the Corsa has the option, but she does not subscribe. It was included for the 1st 3 years of the car, hers is nearly 5, and it's not worth it for her (She just uses apple car play).
The Renault data seems live, but again is on a subscription - this time 5 years, and the car is only 3 - so it's all good.
TomTom in the Fiat, again subscription, 3 years, the car is 2 and its live. We probably wont bother to renew after 3 as that car mostly does local runs.
The Polestar nominaly has a data subscription for 4 years, though I dont think they are charging for year 5 yet. It will go back at that point for a replacement.