Shipping by sea per item mile relative to alternative transportation methods is actually extremely efficient in emissions terms. Secondly, ecommerce might be up but overall consumption is down.
It would still be a net loss in emissions compared to reality but less than a naive "there goes all of that fungible shipping demand forever" model as huge container ships are more efficient in emissions even though bunker oil tends to be dirtier than jet fuel. Plus overall goods consumption is certainly down with COVID.