This seems to be a question that gets asked a lot
AFAIK, there is no "native" (from system settings) way to set up a wi-fi speaker to stream all system audio. There are myriad music-specific applications that can stream music-on-you-computer - see all of those other linked posts for answers around that: but most people want to use a browser-based service (like Spotify, Youtube Music, or Pandora). To do this, you need to run a program that caputures audio and turns it into a data stream. The best application for this used to be Rogue Amoeba's Airfoil for Windows. Unfortunately, support for Airfoil for windows was discontinued.
There are two other programs that will do this. Both use DLNA casting and can capture all audio - your choice of either one application (e.g. Chrome/Firefox/Edge), or all system audio (including alerts). I still own a copy of Airfoil - which still works for the time being. There are two other programs which do the same thing (I have used neither, so can't vouch for either, but have heard good things about both). They are:
SWYH and
Play-Fi.
Hope that helps you all!