> Multi path payments is optional for every wallet I've tried that even has it available
Which wallets have you tried? It's built into LND and turned on by default. So any wallets based on LND should just do it.
E.g. most custodial wallets as well as most nodes-in-a-box (Umbrel, Start9, etc.), plus many mobile phones like Breez, Zeus, Blixt, Bitkit, and ShockWallet.
Multipath payments are also turned on in electrum by default and I suspect they are turned on in the other implementations by default too

