After upgrading to Symfony 7.0, I'm getting:

Fatal error: Type of Tightenco\Collect\Support\Debug\HtmlDumper::$styles must be array (as in class Symfony\Component\VarDumper\Dumper\CliDumper) in vendor/tightenco/collect/src/Collect/Support/Debug/HtmlDumper.php
on line 7

This is probably due to Symfony's more restrictive type handling in v7.

I was able to fix it by adding array at https://github.com/tighten/collect/blob/laravel-5.6-ongoing/src/Collect/Support/Debug/HtmlDumper.php#L14 :

protected array $styles = [

So either upgrading or removing tightenco/collect (as I already suggested at #79) is more urgent now :-)