Netflix has good jailbreak detection and will crash upon startup on an iOS device if it detects your device is jailbroken.

All of the jailbreak detection avoidance apps are defeated by Netflix's detection methods.

However, you can still watch Netflix on jailbroken iOS devices, by doing the following:

1) Add the following Source to your Cydia:

2) Search in Cydia for AppStore++, and install it

3) Open regular App Store, search for Netflix app

4) Long-press (hold down your finger on) the GET button. Wait for a menu to pop up offering you to Upgrade/Downgrade. If this menu does not pop up after 10 seconds, try again. If it still doesnt, reboot your phone and try again.

5) When you get the menu, select Upgrade/Downgrade. After a few seconds it will bring up a long list of versions

6) Select 14.0.0

Netflix should start downloading within a few seconds, and it will now work with your jailbroken device. It will also work with iOS 14, and will not have the iOS 15+ requirement that the present app has.

Basically you are forcing a download of an old version which both works with iOS 14 and doesn't have jailbreak detection.