Your requirements could not be resolved to an installable set of packages.

[finnlewis]

Just tried a fresh install locally and get the following:

$ composer create-project localgovdrupal/localgov-project MY_PROJECT
Creating a "localgovdrupal/localgov-project" project at "./MY_PROJECT"
Installing localgovdrupal/localgov-project (2.0.2)
  - Downloading localgovdrupal/localgov-project (2.0.2)
  - Installing localgovdrupal/localgov-project (2.0.2): Extracting archive
Created project in /home/finn/sites/l.localgov/MY_PROJECT
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Root composer.json requires drupal/coder ^8.3 -> satisfiable by drupal/coder[8.3.0, ..., 8.3.x-dev].
    - drupal/core-recommended[9.1.0-rc2, ..., 9.1.x-dev] require symfony/polyfill-mbstring v1.20.0 -> satisfiable by symfony/polyfill-mbstring[v1.20.0].
    - Conclusion: don't install symfony/polyfill-mbstring v1.20.0 (conflict analysis result)
    - drupal/core-recommended[9.2.0-rc1, ..., 9.2.x-dev] require symfony/polyfill-mbstring v1.23.0 -> satisfiable by symfony/polyfill-mbstring[v1.23.0].
    - Conclusion: don't install symfony/polyfill-mbstring v1.23.0 (conflict analysis result)
    - drupal/core-recommended[9.3.0-alpha1, ..., 9.4.x-dev] require symfony/polyfill-mbstring v1.23.1 -> satisfiable by symfony/polyfill-mbstring[v1.23.1].
    - Conclusion: don't install symfony/polyfill-mbstring v1.23.1 (conflict analysis result)
    - drupal/core-recommended 9.1.0-rc1 requires laminas/laminas-feed 2.12.3 -> satisfiable by laminas/laminas-feed[2.12.3].
    - drupal/core-recommended[9.1.0-alpha1, ..., 9.1.0-beta1] require typo3/phar-stream-wrapper v3.1.5 -> satisfiable by typo3/phar-stream-wrapper[v3.1.5].
    - laminas/laminas-feed 2.12.3 requires php ^5.6 || ^7.0 -> your php version (8.0.8) does not satisfy that requirement.
    - typo3/phar-stream-wrapper v3.1.5 requires php ^7.0 -> your php version (8.0.8) does not satisfy that requirement.
    - drupal/core-recommended[9.2.0-alpha1, ..., 9.2.0-beta3] require symfony/polyfill-mbstring v1.22.1 -> satisfiable by symfony/polyfill-mbstring[v1.22.1].
    - Conclusion: don't install symfony/polyfill-mbstring v1.22.1 (conflict analysis result)
    - Root composer.json requires drupal/core-recommended ^9.1 -> satisfiable by drupal/core-recommended[9.1.0-alpha1, ..., 9.4.x-dev].

[finnlewis]

Note: the composer create-project is working on php7.4 and on @andybroomfield and @stephen-cox's PHp8. So perhaps just a problem on my local php 8.0.8.

Will continue testing.

[finnlewis]

Turns out that this was my local host machine missing required php packages.

See https://www.drupal.org/docs/system-requirements/php-requirements

In my case, I did not have php8.1-mbstring installed.