How do I upgrade to iOS 16 on an iPhone 12?

You wait until it is officially released this fall.

I saw your post and yes. But that can't be discussed in these user forums. If you want to install it, do it at your own risk. If things don't work, you'll be unhappy. You'll be testing software, which can be buggy, but as long as that isn't an issue for you, go for it. Me personally, I need my devices to run without issue. I'm happy for those brave souls who will figure out what doesn't work and I'm perfectly happy waiting until the software is stable and officially released. Note: If you do this and have any issues, you cannot come here and ask for help. You'll have a feedback link, which you'll use to provide feedback, but no one here can help you should you encounter issues. You also sign an Non-Disclosure-Agreement, agreeing to not discuss anything have to do with the software publicly.

See this link --> Apple Beta Software Program

Actually, a number of apps likely won't work properly. They won't be optimized for the new iOS. But yes, Banking Apps definitely won't work, which is yet another reason, I'm happy to wait until official release.

It's also guaranteed any banking apps won't work.

Beta software is not intended for use on any devices you count on for daily use

The bank apps won't work, will give error you have a jailbroken device.

Those I know for sure, as you stated a lot of other ones might not.