What exactly is the problem you are having? I’m guessing part of it might be the dynamic nature of your lists, but having to set a specific range. To deal with that you would be best off setting the max range of the progress bar to 100 and calculating the percentage of completed tasks.
To get your values, I would first create a template column in your tasks sheet of the category and the checkbox value. In the Category sheet, create a template column of the category and the word ‘true’. Then in the category sheet, create a relation to link the category to the category in the task sheet. Create a rollup count using the relation to get the total number of tasks in that category. Next create a second relation using linking the template columns in both sheets. Create a rollup count using this relation to get the total number of tasks that have been completed. Now create a math column that takes the completed task count, divides it by the total task count, then multiplies by 100. This will be the percent complete out of 100.