By default this will disable any fov change entirely. You can tweak 5 fov changing modifiers to your liking using the in-game config editor or by editing the config file.

Minecraft defaults / Config setting:

When flying 1.1 / 0.1

When sprinting 1.15 / 0.15

When using a bow at max draw 0.85 / 0.15

Under the effects of slowness 0.925 / 0.075

Under the effects of swiftness 1.1-1.2 / 0.1-0.2

The mod starts at 1.0, which is your normal fov, and cumulatively increases / decreases your fov based on player state and your desired config settings.

Minecraft is hard-coded to a max of 1.5 and min of 0.1 fov modifier.

Each config setting has a range from 0.0 to 0.5.

This should be a client-side only mod, but I haven't setup a dedicated server instance to confirm it isn't causing any problems.