Note 9

[Arvi15]

Best third party app for app lock

[DamanDhaliwal]

there is samsung official app for app lock known as "S Secure"

[Ravon]

S secure is not available for Samsung s series note series and a series, they crash on install. 

S secure is mostly used for m series and lower end devices

[Ravon]

For Note 9, I think you can go for AppLock by domobile. (It is best for AppLock without fingerprint option)

[Ravon]

Do you want fingerprint app lock or just app lock, and which mobile do you use?.

[KrishnaTurlapaty]

https://play.google.com/store/apps/details?id=com.symantec.applock