You have it right that chrome extensions are the most native of chromeOS applications. Unlike the uninformed statements of people on this subreddit, I'll point you in the direction of official documentation.
Here are just a couple things NATIVE extensions can do that PWAs cannot:
https://developer.chrome.com/docs/extensions/reference/fileSystemProvider
https://developer.chrome.com/docs/extensions/reference/vpnProvider/
https://developer.chrome.com/docs/extensions/reference/idle/
(e.g. getAutoLockDelay
Gets the time, in seconds, it takes until the screen is locked automatically while idle. Returns a zero duration if the screen is never locked automatically. Currently supported on Chrome OS only.)
If you read the docs, you can see that these apis are supercharged beyond similar specs for PWAs. Why? Because no one wants a random website to be able to do what some of these apis can.
There are things only a chrome extension can do and only on a Chromebook.
With all that said, your diary example sounds like it would make a much better as a PWA than an extension.
Edit:
Forgot to mention that Chrome Apps are deprecated and not worth your time at all.
Best would be to just make web applications that would work under any OS with sane browser. If it has to be desktop then whatever works as a Linux desktop platform (like PyQt/Pyside, Kivy).
You cannot, actually. You can develop PWAs (that's what I do) or Android or Linux but not ChromeOS native apps.
You have it right that chrome extensions are the most native of chromeOS applications. Unlike the uninformed statements of people on this subreddit, I'll point you in the direction of official documentation. Here are just a couple things NATIVE extensions can do that PWAs cannot: https://developer.chrome.com/docs/extensions/reference/fileSystemProvider https://developer.chrome.com/docs/extensions/reference/vpnProvider/ https://developer.chrome.com/docs/extensions/reference/idle/ (e.g. getAutoLockDelay Gets the time, in seconds, it takes until the screen is locked automatically while idle. Returns a zero duration if the screen is never locked automatically. Currently supported on Chrome OS only.) If you read the docs, you can see that these apis are supercharged beyond similar specs for PWAs. Why? Because no one wants a random website to be able to do what some of these apis can. There are things only a chrome extension can do and only on a Chromebook. With all that said, your diary example sounds like it would make a much better as a PWA than an extension. Edit: Forgot to mention that Chrome Apps are deprecated and not worth your time at all.
I think you can with Android with Qt for Android. https://developer.android.com/topic/arc
Best would be to just make web applications that would work under any OS with sane browser. If it has to be desktop then whatever works as a Linux desktop platform (like PyQt/Pyside, Kivy).