Write PHP logic in Blade?

It is not. Fetch data through your Controllers and pass them onto views for rendering. If your Controllers get too complex, then consider using Decorators to take on some of the work.

https://laracasts.com/series/design-patterns-in-php/episodes/1

is it good practice to write a lot of PHP logic in Blade?

@gthell No. It completely defeats the purpose of MVC.

Blade template are views. Your pass views the data they need via a controller. Your views should not be doing business logic.

Blade is PHP and if you for some reason need to write custom php you can use the @php directive.

However lite the previous responses it is bad practice to use it to fetch data from the database. If you need to do that one the fly without reloading use JavaScript and fetch it from an API endpoint.