I usually go for virtual private servers, and you can get those for 5€/month on most services (Hetzner in Germany, Scaleway in France, Digital Ocean in the Netherlands and elsewhere, AWS lightsail maybe even in Milan).
For shared hosting, I'd probably consider OVH in France. (but I have not checked if they play nice with Let's Encrypt.)
Altervista is an option too, if you can move your domain with them (check if they give you the services you need)
OVH no. The hosting server are slow compared to italian equivalent offer. And the customer care default response is: this is not our business
check this thread: Web Hosting who support Let's Encrypt
And also the hosting provider table at Does My Hosting Provider Offer HTTPS? | Certbot. They are probably not in sync with each other unfortunately.
I also would like to say I'm not sure if switching hosting provider for your website is appropriate in your situation, as from most points of the world your site is presenting a Let's Encrypt certificate perfectly.
Is that "WIND" thing the sites hosting provider or an ISP providing internet connectivity for a client? Because as I see it, that "WIND" provider is doing a Man in the Middle attack on any connection to your site, right?
Is this ISP blocking/intercepting other sites secured with Let's Encrypt certificates? Like, on a system that's not working to get to your site, can it get to https://helloworld.letsencrypt.org or https://valid-isrgrootx1.letsencrypt.org?
Wind3 is a (very big) residential, mobile and business ISP in Italy.
No, it would be well known if it did so. It's probably domain or IP address based.
So if Wind3 is the problem here, there's absolutely no reason to change the hosting service provider for the site, right?
Yes, it's unrelated to this issue.
It's just the ~1 second round trip to the US for every one of their users that prompted the hosting provider question.
Wow, I didn't realize that—thanks for pointing it out!