It's not so much that manual is better, but that manual is more controlled.

Shooting all the time on full manual will teach you what to do & what not to do. It will take longer & you will probably have far fewer keepers to start with, but you will learn as you go.

If you are shooting full manual, you have to balance up the depth of field you need - aperture - with the exposure time you must have to stop the action, against the ISO necessary to achieve a correct exposure allowing for the previous two settings.

Add to this manual focus, so you could choose in a wide aperture close-up to focus on the flower in front or the face peeking from behind, rather than relying on the camera to make that decision for you.

Running at full auto removes these decisions & does what the camera decides might be 'best' each time… which is rarely is what you actually wanted.

Many photographers actually use "Aperture-preferred" a lot of the time. This reduces your juggling act to fewer parameters. Think of it as 'I can choose most settings, but the camera makes sure the final exposure is reasonably consistent'.

You set your preferred aperture for the type of look you require, quickly check through the viewfinder to see if your ISO is about right to give you the exposure time you need, then you are pretty much back to 'point & shoot'.
Some cameras will override your ISO setting even in this mode, but you can usually switch that off, giving you better control.
I have my camera set up so that my single dial wheel controls aperture alone, but with one of two additional buttons, I can dial in ISO & exposure compensation. This gives me the fastest workflow. Manual/auto-focus is a hardware switch on my lenses, so if I'm sure my focus doesn't need to change for a while, I'll quickly flip across to manual focus. [I also have a focus/exposure lock button, but I don't often use it, as it disengages every time you let go.]