Since you haven't a clue, I'll explain it to you.
Tax evasion is breaking the law by not paying tax owed. Does not apply in to them.
Tax avoidance is avoiding tax by using a loophole in the law. Does not apply to them.
Acceptable tax mitigation is paying less tax in ways that parliament went out of its way to say you are allowed to do. Saving into pensions and ISAs is the way most people do this. Another, that applies to some people with ties to another country, is non-dom status, which lets you be taxed in that country, rather than the UK, on income that was not earned in the UK.
His wife did the latter. Legally and morally, it is equivalent to what you or I do when we save in a pension or ISA.
She (Sunak's wife) did absolutely nothing wrong, but because of a public witch-hunt by a bunch of angry idiots with fuck-all understanding of anything, she was bullied into handing over money earned outside the UK which has fuck-all to do the UK.