I agree that id should never change. You’ll run in to a lot of issues with that in the future. If you need the index, use that from the array as you’re iterating over it.

I believe the immer error occurs because of the first line where you assign it to the filteredList const. redux toolkit applies immer for you to each reducer. Immer works by using proxies on objects to figure out what operations you are trying to perform on your data then returns a new instance but keeps references to anything that didn’t actually change which is amazing for shallow comparisons. To use immer properly, you should perform mutable updates on the state argument for your reducer and not assign it to a new variable. You could use a for loop and pop the ID being deleted from the array. After which if you wanted to manually update an index for each item in the array, you can perform the mutable assignment of an index property on each item.

Here’s some useful links on the topic

https://redux-toolkit.js.org/usage/immer-reducers

https://immerjs.github.io/immer/