In some places. Not in Poland, as long as you're not competing with your employer. Also clauses like "we own the work you do in your personal time" have no lega

In some places. Not in Poland, as long as you're not competing with your employer. Also clauses like "we own the work you do in your personal time" have no legal implications here, because they directly contradict the labor law. Generally you're free to do whatever you wish with your free time outside working hours and the employment contract has no power over it.