You can agree to make it whatever balance you want. 70/30 is a solid recommendation to start with though.

I’ve found that in many cases, because the developers understand what needs to be done so clearly in that backlog that even big items go quickly.

The biggest thing is just to make sure that you’re not in a situation of 100% features where everything else is being ignored until it all catches up to you. 70/30 at least forces the issue.