I did the same last week.
We booked the tunnel for a trip to Normandy in 2000 which had to be cancelled but they gave me a voucher for the ticket for 2021. I couldn't get my money back because I bought the cheap ticket!

but that was OK because we still want to go.
Had to cancel it again last year and been looking at accommodation for the trip this year.
But we keep looking at the ever changing 'entry rules' and the testing you have to do (at the moment) and we are wondering if we should leave it again for this year. I will still be able to 'renew' my ticket & it'll be valid for 2023.
Booked a few weeks & a few weekends in good ol' UK already so not too worried.