Quick take
The OEM replacement is EveryDrop Filter 4 / EDR4RXD1. Use the refrigerator model plus cartridge code when shopping compatible filters.
Correct filter
Whirlpool’s model specifications identify EDR4RXD1 for WRF535SWHZ and list the filter location as interior.
OEM baseline
EveryDrop Filter 4 gives the simplest OEM fit decision and a baseline for comparing aftermarket performance claims.
Compatible filter savings
Aftermarket EDR4RXD1 replacements can be cheaper over repeated six-month-style purchase cycles.
Do not compare on price alone
Check exact model fit and model-level certification before treating a generic Filter 4 replacement as equivalent.