Also some exercises like the deadlift can't be done with an empty bar. Stronglifts would ask you to start with 95lbs which is too much.
To me your comment is toxic and reeks of a sense of superiority and elitism from your own experience. You labelled everyone who can't put 20kg to be someone having a serious medical condition. That's both untrue and disrespectful.
> As you slowly and steadily increase the weight on the bar, you discover places where your form needs improvement.
Please no. The beginner does not discover places where the form needs improvement. The beginner simply fails to lift after increasing the weight. The beginner injures themselves when they thought they could lift but they did not.
The StrongLifts program starting with an empty bar is not right. They should've started with a PVC pipe with the same dimensions as a bar to practice form.
My advice: find a coach and ask him/her to supervise you if you can afford it. If you can't, still find a coach for your first month doing these exercises and then switch to the app.