Cash App offers that feature.
You’re free to use Muun - all I’m saying is that the reality of the situation is there is no way to go from onchain to lightning while paying no fees unless you are using someone else’s liquidity. And that model is less efficient and requires more trust and ultimately more on chain transactions.
I used to use Muun. I tried to send a friend his first Bitcoin payment back in May in exchange for him buying me dinner. But the payment failed, and I was only able to send on chain (which would’ve had a $25 fee)
Fees spikes like that matter much less if you have real lightning channels