If a character rolls a natural 1 on his attack roll, that is an automatic miss "regardless of any modifiers" (page 12, Rolling 20 or 1).

Does that mean that the player cannot use Guidance, Bardic Inspiration etc to modify the roll turning it into a potential success?

That's correct rolling 1 for an attack roll always misses regardless of any modifiers or the target’s AC.

The only game feature that can change that are those making number or result substitution, such as a number for another or miss-into-hit.

I think so, the same if you roll a natural 20. It's a hit regardless of any modifiers or the target’s AC.

Rolling 20 or 1

If you roll a 20 on the d20 (called a “natural 20”) for an attack roll, the attack hits regardless of any modifiers or the target’s AC. This is called a Critical Hit (see “Combat” later in this chapter).

If you roll a 1 on the d20 (a “natural 1”) for an attack roll, the attack misses regardless of any modifiers or the target’s AC.

EDIT: ninja'd by @Plaguescarred :D

There's the classic exception from the Halfling: "Luck. When you roll a 1 on the d20 of a D20 Test, you can reroll the die, and you must use the new roll."

Cool, thanks for that.

That's true for Guidance and a lot of other things, but I'm not sure it necessarily applies to Bardic Inspiration under 2024 rules.

While the 2014 Bardic Inspiration was something you added to a roll when you rolled it, the new one is something you apply after the DM tells you that you failed, "potentially turning failure into success". I think one could argue that it's meant to operate in a similar way to the Halfling Luck feature, where you're retroactively changing the result of a roll. Especially since it it's phrased as "add the number rolled to the d20". 

Compared to Halfling's Luck, Bardic Inspiration doesn't make you reroll a 1, it let you roll a die and add the number rolled to the d20, so if the initial attack roll is a 1,  the attack misses regardless of any modifiers, including Bardic Inspiration.