Pet insurance policies as a rule generally don’t cover for neutering, along with vaccinations, regular checkups, and routine medication (like flea treatment). This is because these things are classed as ‘preventative care’, which can be foreseen and therefore afforded by you as a pet parent.
Some policies might be able to add on a ‘wellness’ or ‘preventative care’ extension to your policy, but make sure you contact the insurer directly to ask about additional pet insurance cover.