Once we open a lightning channel utilizing eltoo / LN symmetry (commonplace 2/2 multisig), the setup/funding transaction should be recorded on-chain in an effort to stop a “double spend” of the funding inputs (and successfully stealing the channel stability).

Nonetheless, what I don’t perceive is why that UTXO, now recorded on-chain, can’t be spent by way of the settlement transaction after the relative timelock has expired. This timelock would in any other case, the way in which I (miss-)perceive it, outline the final word lifetime of the channel which might be very inconvenient.

What am I lacking right here?

Together with the (nice) graphic from Richard Myers as an instance what I imply: