I bought some metal grease, but when I opened the lid, liquid was pooling on top. I think the oil content is separating, should I mix this liquid in?

The thickening agent (individual part) and the lubricating agent (liquid) of metal grease are somewhat separated when there is little movement.
The metal grease has a heavier thickening agent, which tends to separate from the liquid.
When using a harder grease, the liquid should be disposed of (or not mixed) with the metal grease.
For softer lubrication, it is recommended to mix the grease with the liquid.