Mental load is more than chores
Women carried more of the thinking work too.
In a study of 322 mothers, participants reported carrying more cognitive responsibility than their partners for 29 of the 30 household tasks measured. Cognitive responsibility included anticipating, planning, deciding, and monitoring, not only doing the final action.
This was a self-report study of mothers in different-sex relationships. A separate systematic review of 31 papers found the broader pattern was also linked with emotional distress, lower relationship and life satisfaction, and career disadvantages, but its samples were not representative of every couple. Read the quantitative study and the systematic review.