Paolo, having lived in Europe 20 years, I can understand a wish for native keyboards.
Yet Apple has always asked even US/English users to learn a different way for what I see changes on some different Itailan keyboards.
The method to it, and to writing in multiple languagees, is that extra key bottom left: the Option key, between the Ctrl and Cmd. This plus a letter will get you any of the diacriticals I can think of, even Scandinavian ones.
You learn what letter to use for a mark, which is going to be a letter that commonly has that mark in some European language.
To actually get the mark, on any letter that could use it, you type the Option-letter, then the letter you wan to have the mark. You’ll get that letter with the inflection. It’s very smooth.
An example. I want a-umlaut. I type Option-u, and then simply a. I get a-umlaut. Similar for cedilla, etc…
Option-u is likely used for umlaut because of the preponderance of u-umlaut in German text. And etc…
Does that help? I’m looking at an Italian keyboard diagram that reminds me of the Swiss one I used for quite a while – four choices on some keys! In fact I think the Apple way is smoother, and gives more language possibilities, no?
Anyway, lots of languages, and proper basic keyboards for them on recent iPadOS. And the ‘Magic Keyboard’ is, at least for me, wonderful to type on…and stays that way. It feels truly quality.
Clive