required version of swift is not available

[darkoverlordofdata]

I'm trying to build the browser example at https://book.swiftwasm.org/getting-started/browser-app.html , and it says:

Important: Tokamak UI currently is not compatible with swift 6.0+.

however swift.org shows all versions prior to 6.0 as unavailable

assuming documentation may not be up to date, i've tried to compile anyway using the most current version 6.1, and get the following:

warning: failed to retrieve search paths with pkg-config; maybe pkg-config is not installed
warning: you may be able to install gdk-3.0 using your system-packager:
    apt-get install libgtk+-3.0 gtk+-3.0
warning: you may be able to install gtk+-3.0 using your system-packager:
    apt-get install libgtk+-3.0 gtk+-3.0
warning: you may be able to install gdk-3.0 using your system-packager:
    apt-get install libgtk+-3.0 gtk+-3.0
warning: you may be able to install gtk+-3.0 using your system-packager:
    apt-get install libgtk+-3.0 gtk+-3.0
[1/1] Planning build
Building for debugging...
[1/1] Write swift-version-2EDCC7E0106CD24F.txt
Build of product 'carton' complete! (3.86s)

however, no *.wasm file is created

I am able to create and execute the hello world example. so i'm pretty sure the tool chain itself is working.