QT Creator Webassembly: Error while parsing file Test.pro. Giving up

Question

I'm trying to dip my toes into Qt WebAssembly in Windows 10, so I performed the necessary setup as per the Qt for WebAssembly instructions. With that I now have the following installed:

• Qt: 6.5.2
• Qt Creator: 11.0
• emsdk: 3.1.25

In Qt Creator Preferences > Devices > WebAssembly I see the following:

Adding directories to PATH:

C:\dev\emsdk-3.1.44\node\16.20.0_64bit\bin
C:\dev\emsdk-3.1.44\upstream\emscripten
C:\dev\emsdk-3.1.44
C:\dev\emsdk-3.1.44\python\3.9.2-nuget_64bit

Setting environment variables:

EMSDK=C:/dev/emsdk-3.1.44
EMSDK_NODE=C:\dev\emsdk-3.1.44\node\16.20.0_64bit\bin\node.exe
EMSDK_PYTHON=C:\dev\emsdk-3.1.44\python\3.9.2-nuget_64bit\python.exe
JAVA_HOME=C:\dev\emsdk-3.1.44\java\8.152_64bit

which looks like it should be OK from what I can see (note: I downloaded the latest emsdk release from GitHub and used it to install 3.1.25), and it is showing the activated version as 3.1.25.

Going into Preferences > Kits > Kits I can see the C and C++ compiler for WebAssembly Qt 6.5.2 (multi-threaded) is Emscripten Compiler 3.1.25 for C/C++ which also looks to be correct based on everything I've managed to surmise.

At this point I create a new Qt Widgets Application project called Test and tell it to use the Desktop Qt 6.5.2 MinGW 64-bit and WebAssembly Qt 6.5.2 (multi-threaded) kits. Without making changes to what is generated by Qt Creator I can launch the project as a Desktop application and see the empty window appear on screen. However when I switch to WebAssembly I am greeted by an error

<path>\Test\Test.pro:-1: error: Error while parsing file <path>\Test\Test.pro. Giving up.

The project only lists the Test.pro file and nothing else (when in desktop I can see all h, cpp, and ui files). If I try to compile the project all I get is the following error:

Error while building/deploying project Test (kit: WebAssembly Qt 6.5.2 (multi-threaded))
When executing step "Make"

I haven't touched any of the generated files (h, cpp, ui, pro), and am very much as a loss as to what's going on. My Test.pro is as follows:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h

FORMS += \
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

Update

Finally got around to looking into this some more, and it appears to be tied to WebAssembly Qt 6.5.2 (multi-threaded). If I use WebAssembly Qt 6.5.2 (single-threaded) then everything looks to work as expected...