I think that a similar level of intelligence is important.
Capable to get a uni degree but for whatever reason didn't do it, fine.
Uncapable of finishing high school level of intelligence and you have post grad or masters or higher then you are selling yourself short.
This has been my experience. Sex was great, very attentive guy, seemed nice. His highest education was secondary school. He was self employed in a manual job. Beyond the sex, we didn't have anything in common. He didn't understand the meaning of some words that weren't particularly hard.
He couldn't reason or argue a point properly. It reminded me of how I used to think at high school. He was in his 40s. I don't mean immaturity i mean he had a very simplistic way of thinking and a limited vocabulary. Our conversations were truly dull.
It quickly became boring and I was turned off. He made a good FWB but not a good long term partner.
Intelligence isn't exclusive to HE grads but broadly speaking in life your study level represents it and the type of interests and priorities you have in life which are important to align. Higher education absolutely develops your ability to think, reason and express yourself. Nowadays life is too rushed to develop conversation and debate skills, many people didn't grow up discussing issues around the dining table and social media feeds off snappy one liners and txtspk. if you don't actively make it a priority to learn how to converse and to debate, it is so it hard to get good at these without higher education.
If you love reading and learning, maybe going to museums or theatres, maybe discussing politics, ethica, religions, laws or scientific or medical papers and they don't it will be very hard going once the sex wears off.
For example the guy I mentioned would finish work exhausted and all he wanted to do was eat, fuck and watch tele or play video games or do some pranks. He didn't think for himself just repeated what his friend said when it comes to life or politics. At first it sounded like he is intelligent and mysterious with his one liners the I found out that it was because he didn't have or know more so was keen to move on swiftly. The interesting thing that he always went for very ambitious highly educated women even when he had no interest in education for himself or children.