Is it typical for community college to not accept an iep diploma?

AN IEP 'diploma' is not a diploma at all. They call it that to continue the charade that is IDEA which is nothing more that the federal government's permission for your local school district to cheap out on the special school your child really needed to attend. That's what least restrictive classroom is really about. Forcing teachers and other children who are also entitled to FAPE bear the classroom burden so your school district can save money.

not where i live  ...  they have special accommodations for people who need extra support

It varies by state.  There is a state that you don't even need to finish high school, as long as you are 18 you can enroll.

there is no national rule that EVERY accredited college must require an actual high school diploma or GED

Yes. IEP diplomas and HS certificates of completion are not actually high school diplomas. An actual high school diploma or GED is what's required to get into any accredited post-secondary school (i.e., a college or university). So even community colleges, which pretty much all have an open admission policy that allows anyone to enroll regardless of their HS GPA, must still at least require an actual high school diploma or GED, because if they don't, they lose accreditation, resulting in their students not being eligible for federal student aid and resulting in the diplomas they issue becoming worthless pieces of paper.

Yes.  That’s a diploma given to special education students.  Many have developmental disabilities.