Way to early to check this for next year. It depends from country to country. The big timetable change is around the first or second weekend of december. I think the change for most of Europe will be 10 december 2023.
Most timetable information for 2024 will be available a couple of weeks before that date in december, if you’re lucky, a couple of months beforehand.
Reservations vary from country to country, but 2-3 months before the travel day they are available, most reservations should be open for booking. Eurostar is a bit further in advance, that you can book up to 6 months in advance I think. Italy - Spain can be as little as one month before the new 2024 schedule.
The timetable as such doesn’t change that much though, it roughly stays the same, in 95% in varies only in a couple of minutes. If you want an indication of the train services you can expect, search in the planners for next week and plan accordingly for february. Otherwise you’ll end up stressing months, without concrete information.