Can I add a fingerprint without allowing it to unlock the phone? Some of my more secure applications offer fingerprint unlocking. This would be convenient to use, and I don't foresee any security issues with someone using my fingerprint because I would have had to have unlocked the phone with a pattern for someone to gain access to the application.

On the other hand, if the phone can be unlocked with my fingerprint as well, someone could unlock it while I am incapacitated (e.g. sleeping) without my knowledge, and then unlock the high-security applications as well. Having a pattern is a great form of two-factor authentication IMO.

I added a fingerprint to my rooted phone which runs LineageOS 14.1, Android version 7.1.1 -- this automatically allowed unlocking the phone via fingerprint. I cannot find a setting to disable this without removing the fingerprint and being unable to use it in any of my apps. Is there any way I can forcefully disable fingerprint authentication on the lock screen, but retain access to fingerprint unlocking for various apps without using a custom lock screen?

Here are the options I have for the lock screen and fingerprints -- I do not see any way to disable fingerprint authentication without removing the fingerprint, from the settings at least:
The exact thing as you want is not possible on Android.

You can try using a third Party AppLocker App to secure your Applications while unlocking your phone with your Fingerprint, but I would not recommend any uncertified 3rd Party software protecting my apps.