It really boils down to your usage scenario. What is commonly referred to as FDE is really "partition" encryption in which the encrypted container is a partition. LUKS is an example of an encrypted partition.
Encryption protects dead containers. Active use of an encrypted container requires decrypting it, however done correctly the original container is not actually decrypted, a secondary virtual decrypted container is created. This could be an in-memory only file for file based encryption or more commonly a driver interface that performs on-the-fly block encryption/decryption to accessed containers.
Your stated objection to LUKS implies that you are keeping your files on the booted partition that auto unlocks and mounts with startup. If this is not desired, use a separate partition that doesn't auto mount.
In file encryption the encryption container is a single file. Individual files must be individually decrypted for access. Using this for a large number of files can work but will likely be annoying.
The third option is a multi-file container. Instead of a "partition" container or a "single file" container, a multifile container is exactly that, it holds multiple files but is not itself a partition.
The catch in your question is the word "SERVER". If it's truly a server that multiple people are accessing, then either the server must unlock and make available the unencrypted content when running, or each person must unlock content for themselves. It all boils down to the question of who owns the keys? Servers typically need to be able to autostart from power failure or whatever. To do so without manual intervention means that the encryption keys are automatically accessible.