Does Blixt use Bitcoin Core in neutrino mode (compact block filters), or btcd?
That's what I found on the page.
Neutrino node Blixt connects by default to Blixt Server to sync the Neutrino blocks and indexes (SPV mode), but user can also connect to its own node. It is surprisingly sync the whole SPV node in less than 5 min (in my case on Android 11) and I was ready to use the full node wallet (onchain and LN).
I don't believe there's any difference between Bitcoin Core and btcd ever since it was standardized in BIP157 & BIP158.
Blixt uses the SPV client that is also called neutrino to sync from a Bitcoin Core node (node.blixtwallet.com:8333), but it has been served by a btcd node in the past.