Hi. The basic answer is that it is unlikely to help.
First thing to note: You would need to have a Sonos device wired to your router for the Ethernet ports on your Sonos devices to even be active.
Sonos HT systems are designed to communicate within the HT setup using direct routing over 5GHz, so I would not try to frustrate that.
A Boost wired to another Sonos device would probably simply be ignored by SonosNet.
Chain linking Sonos products with two ports so as to achieve wired connections where otherwise devices would be wireless might help if there are wireless issues. Do you actually have a problem?
The best link between the Sub and a soundbar is the dedicated 5Ghz link the system sets up by itself. If you have no trouble now, don’t mess with it.
A Boost wired to another Sonos device would probably simply be ignored by SonosNet.
Anecdotally- I attached a Boost to a Symphonisk bookshelf speaker that was constantly dropping out, and it did seem to improve the speaker's reception. Whether that was to do with the Boost's Sonosnet transmission or the ethernet cable I cannot say.