I really like the sidebar icons but they are limited and I dont know why since basically they are the webpages themselves rendered on a smaller pop up frame when you click the icon, so not much extra developing (e.g for an app ) is needed.
I also use viber and not whatsapp, I also use mastodon and in general why not add gmail hotmail etc so that one doesnt need to open a new tab every time he needs to verify his email address or get a code etc.