https://quoteinvestigator.com/2015/03/04/self-doubt/

We all suffer from "imposter syndrome" (at least the self-aware honest ones) which exacerbates the above.

>I see people posting brilliant work,

Nope; much of it is buzzword-bingo, polishing of superficialities, changing of times, jumping on the current bandwagon and echo chambers. Quite rare to see any real "brilliance".

Think of it as a normal distribution curve which used to be tall and thin now having become short and broad. More people exposed to more ideas and therefore more output to be found but real value has diminished (and whatever little, lost in all the noise which has increased exponentially).

We need to distinguish between Knowledge for Knowledge-sake vs Job-sake and adapt our expectations about ourselves accordingly.