I'm not sure how regulation can hope to really solve this when the problem isn't that an employer is forcing anything on you, but usually more one where your coworkers are independently making decisions about out-of-hours availability that create an unspoken culture, and usual and customary expectations that differ from the official written ones.

You're perfectly free to completely ignore work after 5pm! Nothing bad will happen! A company will swear up and down all day long that they support flex time and you're not expected to ever answer any queries outside of your own working hours!

But if a number of your coworkers decide of their own volition they're going to be in touch at all hours of the day and that becomes the default soft expectation, then you might look worse in comparison. Maybe not in the short term, maybe people will make a strong effort to un-bias themselves during performance reviews and not pay that any mind, but over time, you're sharing the bonus and raises pool with workers who valued their time less than you and perhaps ended up getting higher visibility for it.

Should regulation then mandate that your coworkers disconnect? Maybe. We do it for truckers, pilots, and flight attendants in safety-critical jobs: they're not allowed to work more than a certain set of hours regardless of whether they'd gladly do so.