The tilt changes between about 22 and 25 degrees on a cycle of about 41,000 years. The 23.5 degree number is the average that is the simplified version for children’s textbooks.
~23.5 degrees is not just the average, it’s what it is now, and used for meaningful calculations. It’s not going to change any time soon.
“The 23.5 degree number is the average that is the simplified version for children’s textbooks.”
Well, then, I had better put away my orbital mechanics books and rewrite some equations I wrote since they’re just cartoons and probably not working. /drippy-drippy-sarcasm
The 23.5 is a close enough number for discussions but the Earth is not going to change much from that in our lifetime.