There are enough scientific proof and personal experience showing while I'm losing muscle it starts getting harder and harder to sit and work. Back pain, shoulder pain, etc. no matter how correct I sit/stand.
I hate gym and exercising (even though I used to be a serious gymnast between ages 9-18) but there's no choice but to be active and build enough muscle, otherwise, I can't continue sitting and doing the work I love for long hours.
I'm looking for a reliable, trustworthy, and scientific guide or program for building muscle. I'm not necessarily looking for motivation or coaching, just a proven program that helps me gain and maintain enough muscle to stay healthy. Also, it doesn't need to be an app.
I would suggest picking something that's generally accepted and try it out for a while - if you're going to the gym, learn (with a coach or by yourself) how to do stuff like squat, deadlift, press, bench press and pull-ups and pick a simple program that focuses on getting stronger in these movements.
The book Starting Strength covers this in more detail but you can find articles and videos that summarize it if you don't want to read a book; or you can pick some other program like one of the stronglifts.com progressions - the details of the program don't matter as much as focusing on these main movements and being on a program where you make progress by increasing the weight you lift over time.
https://youtube.com/c/MinusTheGym
Ryan teaches great exercises that require little to no equipment and are great for building strength and muscle.