The latest Sage Advice clears this up authoritatively

Can you concentrate on a spell while transformed by polymorph? You can’t cast spells while you’re transformed by polymorph, but nothing in the spell prevents you from concentrating on a spell that you cast before being transformed.

Since "nothing in the spell" prevents you from maintaining concentration, and taking on the mental stats of the creature you transform into is part of the spell, clearly there are no particular mental stat requirements on the target form required to maintain concentration.

The latest Sage Advice clears this up authoritatively

Can you concentrate on a spell while transformed by polymorph? You can’t cast spells while you’re transformed by polymorph, but nothing in the spell prevents you from concentrating on a spell that you cast before being transformed.

Since "nothing in the spell" prevents you from maintaining concentration, and taking on the mental stats of the creature you transform into is part of the spell, clearly there are no particular mental stat requirements on the target form required to maintain concentration.

The latest Sage Advice clears this up authoritatively

Can you concentrate on a spell while transformed by polymorph? You can’t cast spells while you’re transformed by polymorph, but nothing in the spell prevents you from concentrating on a spell that you cast before being transformed.

The latest Sage Advice clears this up authoritatively

Can you concentrate on a spell while transformed by polymorph? You can’t cast spells while you’re transformed by polymorph, but nothing in the spell prevents you from concentrating on a spell that you cast before being transformed.

Since "nothing in the spell" prevents you from maintaining concentration, and taking on the mental stats of the creature you transform into is part of the spell, clearly there are no particular mental stat requirements on the target form required to maintain concentration.