Can Skilled Worker visa holders in the UK take a second job or run a side business in 2025?

I’m on a Skilled Worker visa in the UK, working full-time as a Design Engineer. I’m wondering if it’s allowed to do a second part-time job in a different field, or even start my own small business on the side.

The new guidance says second jobs must be in eligible Skilled Worker occupations — does that apply to all side work? And what about self-employment or running a business? Or Does this rule only apply to new  visa  holders ?

Anyone have experience with this under the 2025 rules?