In Spain your employee must pay for “after business hours” exclusivity in the monthly payroll. It must clearly state that every month the company pays for the exclusivity. It’s not enough with a contract saying you cannot work after your business hours, they must pay for it and they must proof they are paying it in the monthly payroll.

Not sure in other countries, but probably in Western Europe and 100% sure in Spain even large corporations know it’s really hard to enforce contractual and post-contractual exclusivity, unless the employee breaks some IP of the employer.

Still, it is always a good idea to tell your new employer that you are “moonlighting”.