IMPORTANT: This plugin will NOT function after the Widgets screen overhaul that is part of WordPress 5.8 unless you use the Classic Widgets plugin (https://wordpress.org/plugins/classic-widgets/). The plugin will continue to be supported/maintained for those using Classic Widgets, but there are no plans to make Conditional Widgets work once Widgets are Blocks.
This plugin adds a form to each widget on the Widgets panel which allows users to choose which pages and/or categories the widget is either displayed on or hidden from.
For each widget, you can choose criteria to either SHOW or HIDE the widget, based on a number of categories. The interface is quite intuitive, and requires no knowledge of php or conditional tags.