This is a little tedious at the moment. You can do it through the github integration https://arcade.makecode.com/github which will host a prebuilt version of your game on github pages by making a private repo (it’ll look something like this https://jwunderl.github.io/pxt-scaling/), and it’s also doable through the mkc command line tool https://github.com/microsoft/pxt-mkc.
There was some discussion in Getting rid of the simulator for Itch.io, and I would describe it as a planned feature in the makecode arcade vs code extension (I filed an issue in the currently private repo for that and assigned myself, just haven’t gotten around to it yet as we’re still fixing more prominent bugs / adding other needed feature) and potentially in MakeCode Arcade itself eventually, just takes a bit more time.