You seem to not understand what you are talking about.

First, it's possible to have an app active without spending resources on background windows. This process is called "close a window". If an app has the tray icon available it should be perfectly viable option and, guess what, it works like that with many apps. But no, even the tray menu for Steam is now a damn web-rendered element. Also even in Chromium based browsers, you can have 2 or more windows opened, and when you close one of them you can expect less ram usage than before you closed it. I've seen at least one VScodium derived app that completely unload browser based code when no active windows are visible. You don't need to be a huge corporation to know how to do it.

Second, it's insane to propose that thousands of images from some site (or even from disk cache) are going to be cached into memory immediately upon app launch. You could at least do some research or try Steam app yourself. Want to also tell me how I need thousands of images in my ram even when using Steam small mode?

Third, you mustn't tell me what I need to sacrifice to have "nice and smooth experience". I know enough about code and have seen enough apps to know that you don't need to require GBs of ram from every user to provide good experience. There are literally web based alternatives to CEF that consume 5x-10x less. And then there are many other options for native code.

You mention few megabytes of code. Yeah. Problem is, Chromium code is tons more than that. Those are not "small" apps.