What ads are you referring to? I gave Galaxy S 23 Ultra and I've never seen any ads in the OS.

I am still loving my Pixel 6 Pro. Other than installing AdGuard, or just change your DNS, I pretty much use it as is. I turned off all the Google home or whatever that thing was to the left. Take a minute and go through your installed apps and turn off notifications for things you don't want or just uninstall. I don't think you could ever convince me to buy a Samsung again.

My only gripe is the size and how the camera sticks out. The battery life is great, I have plenty of space locally, and I can wirelessly charge my earbuds with it if I want.

Either keep using your current phone and install GrapheneOS or get a newer Pixel and flash Graphene. It's the best mobile operating system you can find. It doesn't come with any ads, trackers, bloatware, or any other annoying shit. It's just pure Android with many privacy and security improvements.

I currently own a S23+ and had a OnePlus 6T before that and Nexus 5X before that. I wouldn't be bothered by the Samsung bloat. You can uninstall nearly everything. Set the default apps you want to use and hide the rest. You have this configured quickly and then you will never be bothered by it again.

The default Pixel 8 launcher doesnt even allow you to remove the huge Google search widget, which bothers me a lot more. I find One UI pretty vanilla feeling to be honest. Don't notice that much difference from my OnePlus 6T which had a fairly vanilla OS.

I have the Pixel 7 Pro and there's no ad forcing. Some apps can push ads, but just block them or don't use those apps. I'm using the Nova Launcher though. Idk if that matters.

They will hate me but iPhone has BSD/XNU/openSTEP. Of course it may feel like a prison after Android. Either that or a Linux phone with Waydroid

I have the Xiaomi 13T Pro, and I haven't noticed any ads. You can buy wallpapers and ringtones, but there are also tons of free ones, and it doesn't pop up advertisements for it except once to show the function is there. The new HyperOS although it looks the same and has similar functionality on the surface as MIUI, is way way better IMO.
Security and game center are gone, 2 of the top annoyances with MIUI IMO. HyperOS feels way snappier too. With MIUI the 13T Pro was slower than my old Motorola to turn pages in an e-book quickly. Now it's super snappy. HyperOS just feels better somehow.
I installed Firefox with uBlock Origin, and chose it as default browser. I also uninstalled "Community Center" I think it was called. An app to use various Xiaomi services.
There are a couple preinstalled apps, I don't recall if Facebook was among them, but they are easy to uninstall, it literally just takes a minute to uninstall.

But maybe Motorola would be more to your liking, they use almost completely vanilla Android, with only an app to configure Motorola specific features. I did get some ads for printing services on my Motorola, but it seemed to be more a Google thing than Motorola. (Haven't seen any such things on my Xiaomi 13T Pro)
And AFAIK you can still remove the search widget from the desktop on Motorola, something that apparently is no longer possible in completely vanilla Android. Reason enough for me to completely avoid Google Pixel phones. Why would they even want to do such a stupid thing?