Wikipedia says

When using Microsoft Windows, the standard Italian keyboard layout does not allow one to write 100% correct Italian language, since it lacks capital accented vowels, and in particular the È key. The common workaround is writing E' (E followed by an apostrophe) instead, or relying on the auto-correction feature of several word processors when available.

As you seem to be interested in writing in italian with that already has a different set of characters written on it, I recommend you to use a different layout where you have dead keys for diacritis, such as a Portuguese or Spanish layout.

PS: I cannot understand the reason, either. Specially when already providing an Alt Gr key with little use. (On Linux you will probably find many undocumented Alt Gr combinations adding extra characters).

Wikipedia says

When using Microsoft Windows, the standard Italian keyboard layout does not allow one to write 100% correct Italian language, since it lacks capital accented vowels, and in particular the È key. The common workaround is writing E' (E followed by an apostrophe) instead, or relying on the auto-correction feature of several word processors when available.

As you seem to be interested in writing in Italian with that already has a different set of characters written on it, I recommend you to use a different layout where you have dead keys for diacritis, such as a Portuguese or Spanish layout.

PS: I cannot understand the reason, either. Specially when already providing an Alt Gr key with little use. (On Linux you will probably find many undocumented Alt Gr combinations adding extra characters).