macbook security updates for how long?

Hello I want to know if :

1) there is a list of coming updates, and which older devices won’t get them. Because I want to know beforehand if my device stops getting updates so it will because unsafe to use.

2) for a macbook: if it doesn’t get a big update anymore because it’s “old”, (big like sierra to high sierra to mojave), will it still get security updates?

Greetings.