The hurdles for "exempt" are way higher than in the US.
I doubt it is actually done much in practice, although an employee who wants to be left alone on the weekend certainly could. I would also expect that guidance of "don't read your e-mail outside of working hours" would be sufficient to be able to send e-mail to employees at any day or hour without triggering overtime etc.
I sometimes want to send my employees emails over the weekend as I think of something and don't want to forget. But there are certain employees that I know will immediately act on the email, which I actually don't want. So I end up emailing myself and then forwarding them the email on Monday morning.
Certain clients (like Apple’s email app) allow you to schedule emails to be automatically sent at a later date.
This is a you problem. Fix the forgetting part, you are management that's literally your job. Leave a post it somewhere, start keeping a checklist, whatever.
Stop making it your employees' problem.