Just installed iOS 11 on an SE. It turns out I had 33 incompatible apps installed. Five of those I will surely miss. Not essential or irreplaceable, but I really liked them, and now they’re probably abandoned.

Trying to launch an outdated app will bring up the list of all outdated apps.

Does it give you any warning ahead of time that "if you install this update, some apps (or this LIST of apps) will not work anymore" ?

I'd guess not, because Apple is not known for doing anything that might tend to cause users to not upgrade their software or OS.

The only warnings were in the previous version of iOS, “the end is nigh”-style. [sample]

Your comment reminds me of the old joke about the man sitting on the roof of his house praying to be saved from a flood. A truck came by and offered to take him off but he refused because he was convinced God would save him. Later a boat came by but again he refused because "God would save him". As the water rose even higher a helicopter offered to take him off but once again he refused. The water continued to rise and the man drowned. When he arrived at the Pearly Gates he remonstrated God for not saving him. God replied, "I sent you a truck, a boat, and even a helicopter, what more did you want?"

For over a year, Apple has been warning users that support for 32 bit applications would end with the release of iOS 11. They have provided warning popups and a feature in iOS 10 to identify any and all installed 32 bit applications so the user can replace them. They have pulled 32 bit apps from the App Store. I'm not comparing Apple to God but the parallels seem obvious.

I wouldn't plan on using any 32 bit apps with MacOS 10.14 either. The warnings have already begun.

Roaring Apps is a pretty good place to learn the status of various apps vis-a-vis system changes.