Have a look back at
what I said. I said that 1RM is a poor basis
for beginners, because we don't
know their 1RM. They're still learning the movement. Their muscles have a certain strength, but they don't yet know how to fully exert that strength. That's why a beginner may push 40kg today with ease, and have trouble with 30kg tomorrow, or leap up to 50kg, why a slight change in technique will greatly reduce or increase the weight they can move, making it impossible to judge their true 1RM.
As well, it's been shown that in the first three months, a very wide variety of workouts will get the person strength and size gains - fullbody, split, periodised and nonperiodised - almost everything works. So there's no need to calculate things precisely, just get in there and lift and make sure each muscle has been worked.
So
for beginners, it's best to simply go on effort. This is very subjective, the person should feel they've really worked themselves today. And I think that just as the person is learning how to lift, they're also at the beginner stage
learning how to listen to their body. A beginner may push on after vomiting, or they may give up as soon as there's a twinge, and both of those are bad. But part of getting past being a "beginner" is learning to listen to their body, for example when you do a lift and after the first rep are pretty sure of how many reps you'll be able to manage.
What is a "beginner"? If someone is well-motivated and knows what they're doing, or is trained by someone competent, this will be 3-6 months, even sometimes up to 9 months. However, some people are not well-motivated or knowledgeable and have no-one competent training them, so the "beginner" stage can last for
years.
Once someone is past that stage and has achieved some consistency in their lifts and competence in their training, then 1RMs can definitely help, I think - but as always, I don't pretend to know a lot about people at intermediate and higher stage.
For
beginners, we can just go on effort. Get in, learn the lifts, lift as heavy as you can, learn to listen to your body, go home, eat and rest.