Before I saw your reply I actually had another go at rebuilding after removing the Procourse Installer (after doing a git pull) and it rebuilt fine.
I now have another error, but not fatal, with Discourse Dark Mode Theme that I was using - basically it’s not been updated to Ember 5 it seems from looking at Your site may not work because a theme / component has errors which refers to Preparing for Discourse's upgrade to Ember 5.
But since it appears that Discourse now has automatic dark mode available Automatic Dark Mode color scheme switching I can delete the Discourse Dark Mode theme!
Thanks for your help but it appears an update has sorted the problem I had.