Laravel - Request safe method does not exist
Check your laravel/framework version by running
php artisan --version
The safe method found on the FormRequest class was only added in version 8.55.0.
Just good to keep in mind that just because you're on a version 8 of laravel framework, that doesn't mean you'll have all methods and properties found in the laravel 8.x docs. That is unless you're on the current latest version 8 of course.
Using the except() method directly on $request worked. Thanks to @JEJ for his help.
$request->except('thumbnail');