How can a real estate LLC loss from '23 be used against LLC income in '24? Where is this on my '23 return?

The loss on a rental property reported on a partnership return Form 1065 cannot be carried over to the partnership return for the next year.

If you had a loss on a rental activity, it would flow down to the partners by virtue of an entry on schedule K-1. The partner would then determine the amount of the loss allowable on his or her personal tax return and any unallowed loss would be reported on form 8582, Passive Activity Loss Limitations. The unallowed loss as reported on that form would be carried over by the partner to future years as part of their form 1040 filing.

So the unused loss is reported and tracked on the personal return form 1040 along with Form 8582, it doesn't get tracked at the partnership level.

Thanks, Thomas!