The issue is for example, the enchantments. They don't show up. Starting 1.20.5, Mojang has changed the syntax on almost EVERY command including NBT. And It seems that this mod's code is currently outdated due to the issues not only for the /give command but on the commands the use nbt. Just like the /summon command. And most of the time, the autocomplete just, does not show up.

Before 1.20.5
/give @s cobblestone{display:{Name:'["",{"text":"Sus Stone","italic":false}]'},Enchantments:[{lvl:69,id:protection},{lvl:69,id:thorns}]}
After 1.20.5
/give @s cobblestone[custom_name='["",{"text":"Sus Stone","italic":false}]',enchantments={levels:{protection:69,thorns:69}}]

Mod supports 1.20.5 item components and additional suggestions should show up for them (at least they show up on Fabric 1.21 with version 1.3.1). Tell which exact version you are using (mc version, modloader and mod version).

I use
1.21.0
Fabric 0.15.11

I will be back tommorow. My laptop is about to die.

Tell for what exactly command there are no suggestions. Also, if you're using any mods other than NBTac and Fabric API, try without them, and if it fixes the issue, try to find which mod caused it.

As far as I've tested, the enchantments for /give and the entity data in /summon.

It works for me. Do you have any other mods installed?

https://modrinth.com/collection/yXmXu5jp You can check my mod collection.

By the way, Immersive Portals is just there. I have not installed it yet.

I've installed all mods from this collection on Fabric 1.21 including Melody required by FancyMenu and excluding Immersive Portals and WorldEditCUI which doesn't support 1.21, and suggestions still work fine.
If possible, send for what exactly command suggestions doesn't work (e.g. /give @p minecraft:dirt[enchantments={levels:{) as well as Minecraft logs. Also try disabling all resource packs and restarting the game.

Huh, maybe the device? I use MacOS 14. I'll try this again next time.

Maybe, but it still seems weird. As I said, if possible, send Minecraft logs.

Also, I have OptiFabric installed, [for no reason cuz I use optifine and it ain't available on 1.21]

Also, try to use v1.3.1 instead of v1.3.2. Maybe that helps? I still have no hands on my laptop yet.

1.3.2 is only for Forge as it fixes bug present only on it. As for optifabric it isn't available on 1.20.6 or 1.21 so it couldn't cause this issue. If you mean the modpack with the same name, I tried it with mods from your collection and it also has no issues. When you'll have your laptop back, please send logs.

Do you have your laptop now?

Yes, and its resolved. Sorry for the late reply.

Ok, good to hear