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

💁🏻‍♂️⚡️🌽