Firstly, LBTC generally refers to Liquid Bitcoin (or sometimes L-BTC), or even on some exchanges LBTC is for some shitcoin that was deviously named "Lightning Bitcoin".

LNBTC is sometimes used to refer to bitcoin on Lightning network. But all "bitcoin on LN" is bitcoin, so a separate symbol is simply a method to differentiate between on-chain bitcoin and bitcoin on Lightning network.

As far as your question, an answer with a plethora of methods comes from @Darthcoin:

Lightning Network Submarine Swaps https://darthcoin.substack.com/p/lightning-network-submarine-swaps

Also, see another post here on SN which has some good comment replies:

Best ways to convert LN sats to onchain BTC? #100050