Help set up push (with segmentation)

Hello. I don't know if this is the right project category. I set up push notifications from sendpuls on the website. A simple 5-minute integration. I subscribed to the push on my own site. I logged into the send pulse account. And I wanted to see the subscriber filtering. Like on which page of the site the subscriber (like me) subscribed. What category and so on. In short, to segment in order to set up a specific mailing for a specific subscriber. I found nothing at all. There is poor information there. Just the IP. Device type. Windows version. That's it. I wrote in the chat. It was a nightmare, not a consultation. I asked one thing, and they wrote me irrelevant information. After a struggle with 5 messages, they replied to me. For the site to provide such detailed segmentation, you need to additionally add code to the site. And the code they provide is not for push, but like for some email subscription form. In short, probably a trainee operator got stuck. Probably it was necessary to integrate with Gravar. There is a whole article about push with audience segmentation. Here:

https://gravitec.net/ru/blog/targetirovanny-e-rassy-lki-push/#k2

I haven't dealt with them. So I don't know who they are and so on.

Question. Will the audience automatically segment after integration? Or do I need to install any additional codes or some advanced analytics that will transmit some data to the service. 

Also. The subscriber database. Where is it better to store it, with them, on my hosting, or on a firebase account, like securely. Just on various services like send pulse and graver and so on. My database can disappear along with these services.

I can add codes myself. If you have experience. Write what and how. You just need to guide me in this direction. And also answer the questions.

I am set up skeptically, not very much at all. Because there is a desire...
And looking at the present as it is. I see the following. And I don't know if there is any point in all this. I'm talking about push and email newsletters.
Questions:
1. Push notifications without segmentation. People subscribe to push on the site. I don't quite understand. The logic when I see on millions of sites. Subscribe and that's it. And then a million notifications go non-stop to the phone. And I note about everything that can and cannot be. What does an advanced user do in such a situation? They go into the browser settings and delete everything. And then the question is, what's the point of push? And there is no subscriber.
That's why if they are to be done, I believe everything should be made as relevant as possible. So that when I send a push about news and specific news of a certain category. They should be delivered specifically to those people who specifically subscribed to such news. How to set this up? In the article from gravar, the link above mentions something about this.
2. Which sites are successful with push notifications? Can you share, for example. I'm talking about sites from which people do not unsubscribe. And maybe everything is set up relevantly there, and targeted push messages come.
3. After some time, a subscriber database is collected. For example, over 1 - 2 years. And then senpulse is gone. And the entire database is lost. Are such databases exportable? Just because of this, there is a lot of talk that it is better to use Google's tools for push. There is a greater guarantee that the database will live longer, that Google, as it has been for a long time, will not go anywhere. But again, Google probably also doesn't have such advanced segmentation as again in gravar.
4. There are blog sites with millions of visits. And I know from statistics that they have such traffic not only through SEO. But because people are subscribed to them. In the word subscribed, this is email and probably push. If the task is to return an audience of 100,000 subscribers to the site. Then for this you need to pay a significant rate. Stores earn directly from this. And blogs earn pennies from AdSense and so on. So I wonder if a blog can afford such rates if it lives off Google AdSense. It's just interesting. You want to bring back an audience of, for example, 100,000 people. Who will see ads on the site and there will be some earnings. But will it pay off....
That's such a confusion in my head. Because many write words, even Google itself about successful sites. Certain blogs like this: https://mashable.com/
That a lot of people come to them due to subscriptions to the site. About which it does not specify. Maybe push, or maybe email.
5. Regarding email, it's also strange to me that in our time there are still people who will check their email to go from the letter to the blog article link.
I would appreciate clarification and guidance. 

6. Google has started blocking notifications. People often clear their phone caches. Is there still any point in push notifications in 2025, how long do such subscriber databases live? If you have any information, please let me know.