Even only looking at React provided hooks, they added a lot over years and best practices around things like useEffect have changed a lot.

If you have a complex app from 2019 that you haven't updated, it is virtually guaranteed that it has memory leaks and bugs.

I don't really agree that "best practices around useEffect have changed a lot". It's more that that particular hook was used a lot when it didn't need to be so the team finally wrote some guidelines.

yeah same... i have always tried to useState and minimal effects, those have not really changed in 7 years