When typing " or ' the corresponding character is not inserted

It seems like you have the wrong keyboard layout selected.

System Settings->Keyboard, and click the Edit... button next to "Input Sources". Delete any input sources that you don't want to use.

If you use more than one, make sure that you keep the Input source menu in the menu bar:

The US keyboard is almost identical to "US International", with the very exceptions of these "dead keys" used for typing accented characters.

I suggest you switch to the US keyboard, which I gather does everything you need.

This is US:

And this is US International:

Notice the orange-marked "dead keys".

ftomassetti wrote: I am currently using US international, as I did in previous versions of Mac OS without incurring in this issue.

That's really not possible. The US International PC input source is designed specifically to produce the behavior you describe, and has always done so. You just need to remove it and use US or ABC instead (or British if you live there).

It is best not to have any language keyboards you do not actually want to use on your input source list, because it is easy to have them active by mistake.