Yeah Eurostar usually can be reserved up to 11months in advance but due the pandemic they closed almost all trains for reservations until Eurostar is sure the trains will operate :)

B-Europe offer a special website for Thalys and Eurostar reservations but they charge a higher service fee (4€) than Interrail/Eurail (2€) https://www.b-europe.com/EN/Booking/Pass#TravelWish

@rvdborgt posted weeks ago a link to reserve directly via Eurostar itself (they hide the option on their page but it´s still possible if you have the direct link  )

Thank you, seewulf. When I go to Eurostar site they have reservations available for March. It’s just when I try to book it through Eurail that it’s unavailable…

@tmdess 

Eurostar still offer Reservations for Eurail users but they hide the option for some reason :/

The secret Eurostar EurailReservation page.

Thanks. I tried it, and entered my dates, but at checkout it shows the wrong dates. I may just cancel my Eurail pass and buy tickets through Eurostar.

Which website did you try? Normal Eurostar tickets will be more expensive.