Yo yo!

I have very little technical knowledge so please excuse any senseless mistakes.

I want a phone that I can use that is private and secure for the next couple of years. I understand that new android phones will be made differently so I can't side load (whatever that means, I just know it is important). I have an iPhone 12 rn but I'd rather leave the iOS ecosystem. Rn I'm typing this message on a pixel 3.

Is a pixel 3 old enough to still be a safe and secure phone that I can side load apps on in the future?