I also use Muun, there's a big complain about Magnetron (their node) charging high fees on LN.

A non-educated guess tells me it partially has to do with the fact that they use Submarine Swaps (allowing you to do self-custodial payments using your on-chain (BTC) and off-chain (LN) balance interchangeably). If anyone knows any other wallet that can do this and work seamlessly I'd like to try it.

I tried reading about submarine swaps a while back, at a time when I didn't even know what ECDSA was, and my brain almost literally exploded. I'll try to read it again and see if I can get a better handle of how they work.

I use Blue Wallet with my own node and with another LNURLs I use, but only hold lightning balance.