This is because of Microsoft not Ao. Was like this from the past 😋

Lol makes no sense. Why would it be because of microsoft ? the app handles the bring to front not microsoft lol

It is same on web version. Try it. Maybe @klaussinani can work around fix it. But dont make fun of people, u violate code of conduct https://github.com/klaussinani/ao/blob/master/code-of-conduct.md
Also mayde considerered contributting with PR

Well actually no it isn't. The website makes a lot of API callbacks but it's the app that cases bring app to front not the website. I am no blaming Microsoft or @klaussinani, I am just saying that it is a bug.
And I am not making fun of you, I am saying that what you said makes no sense.

I also considered sending a PR but I do not know anything about Electron and Javascript in general, it isn't my field of programming.

I get this too running KDE on Arch Linux.

This happens for me to on Ubuntu 18.04, here's the About:

Version: 6.9.0
Electron: 4.2.2
Chrome: 69.0.3497.128
Node: 10.11.0
V8: 6.9.427.31-electron.0
OS: Linux x64 4.15.0-55-generic

Note I tried using the To-Do web app and it does not bring the browser into focus multiple times, just to clear up any confusion in the above comments.

Same here using KDE on KDE neon. Even if I minimise the window, it keeps on bringing itself to the front which is incredibly unnerving.