The release notes explicitly comments on this. Given the comments it's not really clear that Knots would drop ln fc fee-bump txs.
Ephemeral anchors is a new concept that allows a single dummy recipient
in a transaction, provided the transaction is zero fee and the "anchor" is
immediately sent in another transaction broadcast together with it. This
allows for smart contracts such as Lightning where neither party can
unilaterally increase the transaction fee, yet using an anchor can create
a followup adding the necessary fee. (#30239)
By default, these anchors are accepted by Bitcoin Knots if and only if they
are minimal size and zero value. If you want a more flexible policy
(allowing for dummy sends and/or dust amounts), or wish to reject these new
anchors entirely, you can use the new -permitephemeral option.
There is also a -permitbareanchor option which permits (or forbids)
transaction that do not have real recipients (only an anchor). (knots#136)
-permitephemeraloption. There is also a-permitbareanchoroption which permits (or forbids) transaction that do not have real recipients (only an anchor). (knots#136)