C3sar Hey man, unfortunately Nothing does not provide an official rollback package for OS 4.0 Stable. Rollback is only supported for beta builds, not stable builds.
You either wish that Nothing releases an official rollback page, OR you manually flash an older firmware using a fastboot.
On Adbo and Siemens’ GitHub repo about all Nothing stuff there are some guides about it.
Warning though! You take full accountability of the possibility of bricking your device, while also deleting all your data!
