It is always best to check timetables with the railway company running the train. For the Eurostar between the UK and mainland Europe you can check departure time and pass holder seat availability here:

https://www.b-europe.com/EN/Booking/Pass#TravelWish

The basic service will hardly differ from today/this week-give or take the odd minute early/late. You likely-but why not state clearly- ask this to make a RES/booking. That will only be needed for this €*-any train to Brugge is RES-free.

More of a hindrance then are the last minute Work along somewhere of the tracks-often weekends-these will in general only be released a few weeks or days ahead

BTW: to reach Br from LON: take €* only till LIlle-change (to other station)-again Kortrijk-both legs ev hour with good connection. Just passed by there last FRi

Eurostar releases journeys to pass holders about 180 days ahead so already available to end of April. Use the b-europe site linked above

In Belgium the schedule for next year has not been fully released yet.

Domestic trains in Belgium, are not reservable.

There are plenty of trains between Brussels (Eurostar arrival point) and Bruges. On weekdays 4 trains an hour. It takes about an hour, and won’t change substantially with the new schedule. On weekends there are often engineering works on the line, in which you’ll probably be better of via Lille. But much to early to know something for engineering works for april next year.

Like @mcadv said, you can go via Lille/Rijsel to Bruges, but that involves 2 interchanges. And the train Lille-Kortrijk is only hourly. Brussels-Bruges is usually the better option.