Magnetosphere not in the Quran
Magnetosphere isn't mentioned anywhere in the Quran.
Earth has a visible atmosphere that protects it from meteorites and small debris bombardment. But Earth also has an invisible magnetic field that protects it from cosmic radiations called the Magnetosphere.
Planets having active magnetospheres, like the Earth, are capable of mitigating or blocking the effects of solar radiation or cosmic radiation, that also protects all living organisms from potentially detrimental and dangerous consequences. Wikipedia, Magnetosphere, 2018.
Without this magnatic field life would be impossible on Earth's surface.
[Quran 21.32] And We made the sky a protected shield and they turn away from its sign.
The visible atmosphere sheilds Earth from meteorites and small debris bombardment. But to understand why this verse said a "protected shield" you have to look at Mars. Mars had an atmosphere however it lost it because it didn't have a magnetic field. However Earth's atmosphere is protected by this invisible magnetic field. This is why this verse said "protected shield" because this atmosphere (our visible sheild) is also being protected.
How could an illiterate man who lived 1400 years ago have known that Earth has a protected shield?
The verse, even in the apologetic translation, doesn't say anything specific:
And We made the sky a protected shield (سقف) and they turn away from its sign.
The claim that this verse is specifically about the magnetosphere is unsubstantiated.
Apologists translated the word سقف (saqf) as "shield". However it is commonly translated as "roof":
Dr. Ghali: And We have made the heaven as a roof well-preserved, and (yet still) from its signs they are veering away.
Muhsin Khan: And We have made the heaven a roof, safe and well guarded. Yet they turn away from its signs (i.e. sun, moon, winds, clouds, etc.).
Pickthall: And we have made the sky a roof withheld (from them). Yet they turn away from its portents.
Sahih International: And We made the sky a protected ceiling, but they, from its signs, are turning away.
Yusuf Ali: And We have made the heavens as a canopy well guarded: yet do they turn away from the Signs which these things (point to)!
Mufti Taqi Usmani: We made the sky a protected roof; and they are averse to its signs.
The sky is not "a roof", therefore the verse is rather a scientific error in the Quran.
Tafsir al-Jalalyn explained the verse this way:
And We made the heaven a roof for the earth functioning like the roof of a house preserved from collapsing
The translation "a roof" is also supported by another verse where it is connected to a building:
Those before them had already plotted, but Allah came at their building from the foundations, so the roof (سقف) fell upon them from above them, and the punishment came to them from where they did not perceive.
The usage of the word "roof" also indicates that the world is flat (see Flat Earth and the Quran).