Is there a word or expression for someone who knows various things, a little bit of everything, but is not specialised in anything? [duplicate]

They're a jack of all trades. Some might add and master of none.

"Jack of all trades, master of none" is a figure of speech used in reference to a person who has dabbled in many skills, rather than gaining expertise by focusing on one.

Such a Jack of all trades may be a master of integration, as such an individual knows enough from many learned trades and skills to be able to bring the individual's disciplines together in a practical manner. This person is a generalist rather than a specialist.

- wikipedia

If you are looking for a term that describes a person as not being a specialist, but doesn't necessarily place any limits on their level of skill, then you can call them a generalist.

Generalist
Noun

One whose skills, interests, or habits are varied or unspecialized

^{Merriam-Webster}