Thanks for clarifying, and for curing my misunderstanding.

Hmmm. Whatever the problem might be, it's none of the common causes: Wrong sources and non-Ubuntu packages. Kudos for doing things the right way and for staying on top of maintenance.

Were it my system, I would run a 24.04 LiveUSB, enter the 'Try Ubuntu" environment, install cacti, and test if my customizations work in the updated environment. Knowing that answer will give you options to move forward,