ALE-70.

This is coolbert:

Concern ourselves here not so much with the F-35 warplane but the internally carried ALE-70 countermeasure device. Towed behind the aircraft as a decoy. Protection against enemy radar guided missiles.

"Take A Look At These Photos Of An F-35 Flying With The ALE-70 Towed Decoy Door Open"

From theaviationist.com the article by DAVID CENCIOTTI November 29, 2022.

"The ALE-70 towed radio frequency countermeasure is stored under a hatch next to the dual infrared countermeasures dispenser doors, that appear to be open too."

[....]

Click on image to see an enlarged view: "Towed decoy systems are used to protect military aircraft from radar-guided missiles. These countermeasures are towed behind the host aircraft protecting it against both surface-to-air and air-to-air missiles. They provide a radio-wave reflecting bait that attracts the RF-guided missiles away from the intended target. They are attached via a Fiber Optic link that is used to send commands to the decoy radio frequency emitter to produce jamming signals required to lure the missile away from the 'parent aircraft'."

True and fully complete stealth capability of the F-35 only realized when munitions and associated devices such as the ALE-70 carried internally.

coolbert.