Powerful Horizontal products like Notion, Airtable, Excel, and Roam are all powerful/flexible and require learning and expansion of use cases over time to wrap your head around them. Given that, why do they only teach people how to use the app for the first few minutes?
User goals change over time. The goals that users have six days in are going to be different than the goals they have 6 months in, so it needs to be the case that User skill level increases over time in order to match their changing goals. Apps with continued user involvement respond to changing user goals over time, so the app should continuously teach people how to use its app better. Additionally, product teams will often add new features that expand the app's possible use cases, requiring the user to learn something new after they may have thought they were already done learning.
Continuous onboarding is an onboarding that never stops. Users continue to improve their Self-efficacy using the app, progressively enhancing their utility of User Involvement over time.
It should be noted that some apps have a more expansive range of potential use cases than others. It may be the case that the user can learn your app in 10 minutes and then be done learning. The important thing to continuous onboarding is to think about Goal Resonance- how will a user discover that the app helps them accomplish a goal and execute the sets of behaviors that enable them to accomplish said goal? The user may have a lack of imagination as to what user goals they can accomplish, so how can we expand their conceptualization of the product's utility?