Just click the uBlock icon, select the "element picker" and click on the element you want to remove. You will get a preview and when you are satisfied it will b

Just click the uBlock icon, select the "element picker" and click on the element you want to remove. You will get a preview and when you are satisfied it will be saved to your preferences and you will never encounter that popup again. You could also click the "</>" icon instead to disable Javascript for the site. Substack has subdomains for every site though so you want to click the "dashboard" instead, go to "My rules" and enter "no-scripting: substack.com true" to disable it for all their subdomains. It used to show an irritating please turn on javascript-message, which can be removed in "My filters" as "substack.com###nojs-banner".