A channel must be funded in order to open it. That's one onchain utxo. It is probably some kind of multisig magicwhen you use self custodial but not self hosted ln wallet. I don't get this completely either but ok. π
Depending how much you funded the channel you'll have inbound and outbound capacity, so as long as you transact within this range nothing happens onchain only when you close the channel - to withdraw you funds - you deal with utxos again. The same with the ten people who want to send you 21 sats they also have channels funded etc. etc.
Only channel open and close happen onchain, the zappening in between is only on lightning nothing to do with utxos.
I have blindspots too but I hope it helps a little.