It’s only 1% of my gross income (before tax) as a freelancer. I’ve never seen or heard of it being exercised in my sector (management consulting / cyber), but to be honest it’s a small price for peace of mind in case things do go pear shaped.

Is that liability, or also Errors and Omissions?

IIRC, Errors & Omissions insurance is often called "professional liability insurance".

Exactly, many businesses require this anyway, like if you lease an office.