I use Opera sometimes and it's not bad. I saw they even offer free VPN, does anyone here know safe to use it?
No. Don't use it. It makes your privacy worse, not better. Take a look at Opera's Privacy Policy here:
https://www.opera.com/privacyWhen you install an Opera application, a random installation ID is generated. We may collect this identifier, as well as your device ID and hardware specification, operating system and environment configuration, and feature usage data.
We use this information for certain legitimate business purposes, namely:
To understand better how people interact with our applications and services;
To enhance, modify, personalize or otherwise improve our applications and services;
To determine the effectiveness of promotional campaigns and advertising;
To detect, debug and fix crashes in our applications and services;
To prevent security breaches and abuse.
Based on advertising IDs and your general location, some of our mobile applications may serve targeted ads. These ads are provided by our monetization partners. You can always adjust your personalized ad choices in the application’s “Settings” menu or through your operating system’s settings.
We collect this data pursuant to our legitimate business interests.
Emphasis mine. They monitor your usage and share that information with ad companies to personalize the ads they target you with. Also take a close look at the "Third parties" section on the privacy policy I linked to. Third party code is included in their products from a variety of companies, including Google and Facebook, the two biggest privacy invading companies out there.
If you are getting something for free, then you are the product. Companies have to make money somewhere or else they will cease to exist. In the case of "free" VPNs, the providers are harvesting and selling your data to any number of third parties.
BTW, does it really matters which browser I use on Android when it's full of Google apps collecting all information about me?
You could look in to installing an open source operating system such as GrapheneOS or LineageOS. If you don't want to go down that route, then you can use an app such as
NetGuard to prevent various Google apps from phoning home all the time.