What do you do for an LLC that was not used on 2023 at all

Did you close for good or just for a year?  Do you have assets?

If it is a single member LLC that is a disregarded entity, then for federal tax purposes, if you just had an inactive year, you would not do anything.  Then if you have income again in 2024, then you would include the income and expenses on your return for next year.  If you closed for good, and had assets that you need to dispose of, you would file a final return and include form 8594 with it to dispose of the assets either by selling them or turning them into personal use.  

If you are filing a 1065 as a partnership, then you would need to file a return showing no activity for the year if you plan to resume activities.  If you are closing for good, then you will need to file your final return.

For both the partnership and Single member, there is a box to check as you walk through the business questions to say that the business is closed.  If you select this box, TurboTax will walk you through the rest. 

The above information is for your federal return. State rules vary, but you may have additional reporting requirements with your state.