So thanks to #[0] I have just discovered the cheapest (but not the most private) way so far to move Bitcoin on Lightning to an onchain address. Caveat: you need to have access to Strike.
1) send BTC to Strike via Lightning
2) switch to the Buy/Sell BTC section on Strike
3) use the cash that Strike gave you when you completed step 1) to buy BTC
4) send BTC to onchain address with no fees
ππ»ββοΈβ‘οΈπ½