It seems that you among many others get your strength training information mainly from videos on youtube and in your case primarily from videos by Jeff Cavaliere.

I think Jeff Cavaliere is a very knowledgable guy that could easily create a great 1 hour video that would learn a beginner much of what he/she needs to succed in strength training.
 
However that is not how youtube works.
In order to make money from youtube you need a lot of views. 
The way you do this is by creating a lot of short but entertaining videos. You spend little time on making each video. You do not care about the overall understanding someone gains from watching the videos. Instead you focus on minor details and claim that this is important. Further it helps to make dramatic claims like "this and that is killing your gains" since this attracts people's attention. 

Instead I would suggest you read one or more books on strength training.
I can recommend:
- The Art of Lifting (Nuckols and Isuf) 
- Maximum Strength (Cressey)
- The new rules of Lifting (Schuler and Cosgrove)

One important takeaway from these books is that one should prioritize compund movents such as squats, deadlifts, push-ups and pull-ups that train many muscles simultaneously. After having completed these one can use isolation exercises to hit the remaining muscles. 
If one do it the other way around and start with the isolation exercises (small pebbles) there may not be "room" for the compound movements (big rocks):
[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/yfFsl.png