This is the MuscleMeron Training Program which I think is the most efficient for building muscle without spending too much time in the gym. Just 2x a week for about 1 hour per session or even less.
Many programs circulating on the internet don't work because most of the people selling the programs have used steroid drugs for their bodies. So their programs won't work for people who haven't used drugs.
That's why they can workout almost every day because they took drugs to make their muscles grow faster! If a person doesn't have steroids and is natural, they need more rest.
They are like 45-day steroids chickens that grow from chicks to full-grown chickens! But native chickens that are naturally without steroids will take 6 months to reach their full size!
Steroids are not good because you will get sicker and lose your hormone balance. You will die faster. But we will talk about that in more detail later.
In short, a real program for drug-free lifters has adequate recovery time. That's why only 2x per week to rest. Because the real muscle growth is during rest time, not in the gym!
My body is better now that I don't workout all the time. Only 2 times a week but intense so that there is a reason for the muscles to grow. Then I continue to get stronger and bigger over time.
The good thing about this is that it can work especially when you are older. 40 years and above, you can still do this and get good results.
Natural, no drugs and safe. Healthy for the long term!

Here's an overview of the training program and how to create your own version using various methods:
Download it so you can understand how the program works and you can create your own version.
This is the Barbell edition for people with access to a barbell:
This is the Bodyweight or Calisthenics edition: