You're right, though I consider that the workaround and not the actual solution.

Also, some apps cannot be disabled depending on the vendor. e.g.: Weather (which launches random notifications from time to time), Radio, etc.

To use Whatsapp only, without all the other useless features, try using Beeper. Also works to use instagram messaging without having the instagram app itself, therefore no doom-scrolling. It's open-source.