What a feature to introduce in 2020. This has been a core part of the UI of OS X for… ever? For every app.
Simpler, more elegant, better integrated solution, consistent across the whole OS.
"Asterisk in the Title Bar" is a very unrefined solution to the problem.
Not saying it's better, just that your "unrefined solution" might be another man's "feature".
It shows up on the titlebar but more importantly in the window pager/taskbar, which isn't a feature on Mac OS (though to be fair it also doesn't show up on Linux/Windows desktops that are configured to show icons only in the window pager).