Hi @spurs2
I understand you are using the latest Laravel 9 and possibly the latest PHP
However the set up should not be different to set it up on IIS with PHP 7 and older Laravel versions.
So the information you find regarding PHP 7 should also apply
ok back to the specific error you received "cant append permission"
Does this show on the browser as a laravel error? or you see this on the Windows file explorer.
If is a laravel error then possibly you need to make sure the user IUSR have access to the storage folder.
I was able install a fresh Laravel 9 application on IIS and see the start page.
My system = IIS 10, Windows, PHP 8.2, Composer 2.3
Steps
1 - Open a terminal then cd into "C:\inetpub\wwwroot" iis application folder
2 - composer create-project laravel/laravel spurs-app
3 - Go to IIS navigate to default sites and create a virtual directory to point to your new app
C:\inetpub\wwwroot\spurs-app\public
4 - Add a web.config inside the public folder
You can refer to this for web.config details
https://laracasts.com/discuss/channels/servers/iis-8-laravel-webconfig
If the issue persist, try and paste the error text for better debugging.