A warning: the cheap air monitors don't monitor particle count, just CO2. If you're allergic to pollen you expose yourself to it by opening windows. I've had to help a couple friends who used this and ended up sneezing and sniffling like crazy.

I have the Dylos monitor which does monitor particle count so you can see it drop when your air filter is working https://www.amazon.com/dp/B08F2YM8SM/ref=cm_sw_r_apan_glt_i_...