The filter has one job
The removable filter catches part of the airborne dust before it reaches the internal components. It should be checked and cleaned according to the manufacturer instructions, but it is not designed to clean the rest of the unit.
What sits behind it
The indoor airflow path also includes the coil, fan barrel, drain pan, louvres and housing. Those areas can collect material over time, particularly in systems that run for long hours.
Use condition, not assumptions
If airflow remains weak, a musty smell returns or buildup is visible after the filter is clean, photograph the condition and arrange an appropriate inspection rather than spraying household products into the head unit.
The practical takeaway
A clean filter is a good start. Persistent signs after filter care are the reason to look beyond the first layer.