Do you have a CO2 monitor? I bought one during Covid to monitor the classroom I teach in. I was surprised by how bad it got: well over 1000 ppm.

When I brought the monitor home, I was surprised all over again by 1000+ ppm levels with just a couple of people and a cat. All the efforts to seal the house for energy efficiency were in direct opposition to advice to lower CO2 levels. The only reasonably effective solution that isn't absurdly expensive is to open the windows a little. All the time. You pay more on heating and cooling, but.. there is no alternative.

The good news is that it gives you a reason to leave the drafty window air conditioners installed all winter long.

And house plants have negligible impact on the levels. Keep plants for the aesthetic, but they aren't going to solve the problem.