Silver llama symbol

It’s an icon placeholder. Do you have mods installed?

Its a placeholder for traits via mods. I guess you are using the playable pets mod? Its one of my must-haves besides MCCC :)

EA never intended for pets to be controlled in Sims 4. There's no cheat built into the game either. This means pets don't have a proper set up like a normal sim would. The mod you're using only gives the ability to play pets as others have mentioned.

The llama is a placeholder for several hidden traits the game assigns your pet randomly at creation. Things like Afraid of the doorbell and Likes to swim.

With this mod you can see what they are (the mod is an addon to Selectable Pets that you already seem to have): https://modthesims.info/d/603768/hide-or-reveal-pet-quirks.html

Choose one of the two files only:
PetQuirkswithNames replaces the llama icon with the pet's hidden traits
PetQuirkshidden will remove the llama icon (but you won't be able to see what your pet's hidden traits are)

It's basically a 'blank' for when the game can't find what to put there. So from your image, I would guess that all those traits are just blanks now.
It doesn't only happen just with mods, an update/patch can confuse the game and give a 'blank Llamma' until you chose the same trait again. ;)

Thanks everyone for helping me understand what this was, you're right it's the selectable pets mod. I forgot I had it installed, I removed the file to see if it removed the symbol which it did, then quickly added it back when I realised how much I use it, game doesn't feel normal without it now lol