MacOS/Windows
The process is almost the same as on the Raspberry Pi, it's just a container to start.
Install Docker Desktop
You first need to install Docker Desktop.
Follow the instructions on Docker website.
Docker Desktop should install Kitematic, a Docker GUI. If it doesn't, you can install get it on Kitematic website.
Start Gladys
You need to start Kitematic first.
Then, search for "gladysassistant":

Select the tag "v4-amd64":

Click on "Create" to start a new container:

Then open in your browser the address showed by Docker (here, "http://localhost:32768")

Success!