Q4_K_M is the "default" for a lot of models on HF, and they generally require ~20GB of VRAM to run. It will not fit entirely on a 16GB card. You want to be about 3-4GB VRAM on top of what the model requires.
A back of the envelope estimate of specifically unsloth/Qwen3-30B-A3B-128K-GGUF is 18.6GB for Q4_K_M.
???
Just run a q4 quant of the same model and it will fit no problem.