Custom certificate is a developer option available for users with the huge or giant donation that allows signing clones using your own signing certificate instead of using the default unofficial platform certificate.
Supported keystore types are JKS (the default Java keystore type), BKS (BouncyCastle keystore) and the PKCS#12 standard. After loading the keystore, depending on the keystore type you will need to provide the keystore password, the key alias and/or the key password.
The certificate configuration is stored internally in an encrypted manner and cannot be exported as part of the clone settings, nor may the certificate be recovered by importing the clone settings from a cloned app.
You may configure a global certificate under the App Cloner Settings, in which case the certificate will be used for all cloned apps, or override this per app using the developer option Custom certificate.
Note that if existing clones were signed using a different certificate they need to be uninstalled first.