Removable Media settings tattooed to device

Yes, that key is the exact location Intune writes when you enable Device Restrictions → Removable storage → Block (Deny_All)

ADMX‑backed profiles are "tattooed": once the profile is un‑assigned Intune stops managing it but "doesn’t revert the value", so the block survives reboots and the key gets re‑created on every sync 

Deleting the key manually won’t help—you must push a new policy that sets Deny_All = 0 (or marks the setting "Not configured" via a fresh Device‑Restrictions or custom OMA‑URI profile). After that profile applies and the device syncs/reboots, USB storage is allowed

Apart from this key, only HKLM\SYSTEM\CurrentControlSet\Services\UsbStor (Start) or Defender Device Control rules could still block USB, but they’re not modified by this setting.  
If you can’t deploy a “clear” policy, the last resort is a wipe/re‑image, because the tattoo won’t fall off on its own.