I think most marriages and partnerships struggle with this stuff - especially when one person (due to logistics, work flexibility, gender roles, or whatever) becomes the default primary caregiver.
The way we have broached this subject in my household is discussing the burden or mental load of visible AND invisible work, and occasionally working to re-calibrate with open communication. Using these terms, we've been able to more equitably factor the workloads. Its impossible to keep balanced 50/50 in all things, all the time (work hours, childcare hours, liesure hours, housework etc.), but the occasional discussion/ back of the napkin tally of visible and invisible work loads helps us when we need re-balancing.
I hope this framework might be helpful in your discussions. It's challenging to aim for constructive conversation and avoid tit-for-tat-ness!
Visible: work hours outside the home, preparing meals, housework/ cleaning, childcare taking (meal prepping, laundry, supervision, drop offs/ pick-ups, etc.), running errands (groceries, etc), and visible forms of leisure time, quality family time
Invisible: mental work of managing housework (having the innate sense that its time to change the sheets, clean the bathrooms, etc. even if these tasks are delegated out), the mental work of meal planning, mental load of managing the finances, mental/social work of managing childcare (daycare emails, class parties, planning play dates), emotional work of managing social ties (usually one person in a relationship tends to be the default keeper of all things social responsibilities, IE extended family member's birthdays, mailing cards, picking up presents, planning family trips, staying in touch with family friends, etc). Basically, less overt but still very real time, tasks or mental space that's occupied by family or household planning.