The future is the tense used to predict or express future events.
We use the future simple to express spontaneous decisions, opinions and hopes {see Future Simple, A2 level}.
Be going to is used to express intentions for the future and make previsions based on signs we see at that moment {see Be going to, A1 level}.
https://open.books4languages.com/english-a2-grammar/chapter/future-with-will-or-be-going-to/