Your iPhone can be turned into a dumb phone
One of the common and valid complaints I hear from folks about the modern dumb phone hardware options is that there are essential apps that you can't live without that aren't available on a dumb phone - Ultimately, this means you either cannot switch to this hardware or you have to make those necessities someone else's problem.
There is another way though: You can use Apple Configurator to create a moderated, managed iPhone device that has features disabled that you do not want to use. You can even set it up to make it so, when the profile is applied, you cannot access the App Store from your phone.
I have been using this combination of tools for over a year now to control what I can and cannot do on my iPhone. By managing it and removing the App Store as an option, downloading new apps (and updates) is just inconvenient enough that I don't bother 99% of the time to do so unless absolutely necessary.
You can also turn off other essentials like FaceTime, iMessage, AirDrop, iCloud. You can prevent every USB connection to the iPhone from succeeding except for the computer on which you setup your profile, which is both a great privacy/security feature and a really good way to prevent you from circumventing yourself.
So, if you do this method, remember you have to start fresh with a new iOS install on your phone, and you should start the setup by setting up the phone with configurator. There's tons of guides to do this, and I'm contemplating writing one myself, too.
Setup the configured iPhone, and before applying the restrictions in the profile, wait a week or two. See which apps you need in your daily life. Install them as they come up. Once you feel you have everything you need, then apply the profile that prevents you from downloading more.
I am surprised how little I use my iPhone today, but how easy it is for me to still do all the essential digital things I need to do these days when I have to. In my opinion, this is a win-win.