Spoken Content, Speak screen and speak selection stopped working propperly with the Siri voices in my iPhone 11 after installing iOS 18

Hi everyone.
Wondering if someone has the same issue, or am I the only one?
I have an issue with Spoken Content in my iPhone 11; Since I installed iOS 18, when I select the Siri voices to hear any text, the speech sounds a lot more robotic and monotonous, compared to iOS 17. I can see that the voice file weighs 47.7mb, and this number is also shown in my iPhone 13 that still has iOS 17, however, it sounds excellent, very natural and realistic in the 13.
I’ve also check the VoiceOver settings while using the Siri TTS for both, and I’ve found interesting results: It uses the same voice file for both, VoiceOver and spoken Content, however, this doesn’t happen with my iPhone 13 because it uses a separated voice file for each of those functions, and I assume that’s the reason why the Neural engine voices aren’t working.
I’ve done everything I can think of, since re-downloading the voices to reset my phone to factory state and set it up again, but nothing has solved the problem unfortunately.
I spoke with Apple Accessibility support numerous times, but nobody knows how to help me with this situation apparently because none of the agents speak Spanish.
Now, I can’t try to install iOS 17 to make it work reliably again. I really need this feature to read Image descriptions, listen to my notifications and Webpages in other apps, since the Safari built-in Listen to page features relies on Siri, and it uses the neural text to speech, but that robotic Siri voice really annoys me.
Is there a way to fix it?
Any fix, workaround or suggestion is highly wellcome.
Thanks