Aris, you're on the right path, but you've strayed off into the weeds.
You seem to be confused on what data gets sent to your server when and how. There's other methods, but for our purposes with WP, we can say all data is sent by browsers by one of two types of requests: GET and POST.
Links are always GET requests, the only data sent must be in the URL itself, other than some header data, nothing else about the page is sent. In particular, the form data is not sent. The PHP page receiving the request can get parameters in the URL as parts of the $_GET array.
Form data is sent by what ever method is specified by the method attribute in the form tag. The data sent is the names and values of all form elements within the form tags, nothing else. If the method is GET, each form element's name becomes an url parameter that is equal to the element's value. Forms with many fields result in very long URLs so this is often not a good method for forms.
Forms are better sent with the POST method, in which case the data is sent in a separate data packet than the URL and is retrieved in PHP as the $_POST array. Again, only the names and values of elements between form tags is sent, and there are no URL parameters at all.
So now you should see that the nonce in your form will never be seen when the delete link GET request is sent. Now that you have a nonce check in place, it will always fail. You need to build your delete link with wp_nonce_url(). Then the nonce check will actually have something to check.
But don't get rid of the form nonce! Just as much as you should ensure the delete request is from a proper source, you should ensure the insertion of data request is from a proper source as well. But use a different nonce name to avoid confusion. (I know,.. Arrrgh! More work!)
I know all this security stuff is a lot of bother for just a simple delete request, especially when you're learning. Unfortunately, by installing WordPress, you've made your site a target for hack attempts. Fortunately, the core WordPress is very secure, but you need to do your part to maintain it when you extend it's capabilities. Especially if others will be using your code. If you don't, somebody will eventually find the hole. Once you get this all figured out the first time, writing secure code will become second nature.
Keep up your worthy efforts. I hope you are finding some enjoyment from this.