This mod adds a highly configurable zoom button, as of Ok Zoomer 2.1.2, it works on Fabric 1.15.x (and the 1.16 snapshots) and requires the Fabric API in order to work, you can install Mod Menu in order to easily configure the mod without restarting Minecraft.
By default, it behaves like OptiFine's zoom, but there are a lot of extra features that can be enabled or disabled in the mod's config like:
The classic smoothiness when looking around, but unlike other zoom mods, it works very well along with Minecraft's Cinematic Mode, the only change to it is that holding it down will no longer toggle the Cinematic Mode multiple times, but it shouldn't matter on normal usage, it's on by default.
If you aren't really a fan of the smooth camera but still want something to slow down your aim, this option is for you, inspired by WI Zoom instead of OptiFine, this option will reduce your mouse sensitivity according to your zoom multiplier, being more precise than Smooth Camera. NOTE: You can enable both Smooth Camera and Reduce Sensitivity, but aiming will be definitively worse.
While enabled, zooming will hide your hands, just like OptiFine, this feature does what it's supposed to do, it's on by default.
When zooming in and out, there's will be a transition between the two states when this feature is enabled. It's highly recommended to enable this option, specifically if you have zoom scrolling enabled. This is off by default to match Optifine's zoom.
It's like the accessibility option for allowing to toggle sneak/sprint, but for zooming, when enabled, it allows for toggling the zoom instead of having to hold it, pretty straightforward, it's off by default to give the OptiFine zoom experience.
When this option is enabled, you can increase or decrease your zoom by using your mouse's scroll wheel, you can change the limits by changing the minimum/maximum zoom divisor in the config. It's off by default.