In the Steam settings, to use Proton you need to enable it in the “Steam Play” section. Doing this will enable the Proton translation layer and allow you to play (most) Windough$ games on Linux
I usually use Proton Experimental in the dropdown since it seems pretty stable and keeps it up-to-date.
*And enable Steam Play in the settings
And a lot of linux programs take inspiration from Microsoft’s design because they’re the norm. When you think of a word processor you think of Word, same goes for all of Office 365 actually.