A bit late to the party, but I just tried #12653 and noticed some non-intuitive behavior (on macOS), that's probably worth explaining release notes and help.

Before this new feature I kept the entire datadir on an SSD drive, so I launch with: `bitcoind -datadir=/Volumes/SSD/Bitcoin`.

Initially I naively moved `/Volumes/SSD/Bitcoin/blocks` to `/Users/bitcoin/blocks` and added a line to `/Volumes/SSD/Bitcoin/bitcoin.conf`: `blocksdir=/Users/bitcoin/blocks`.

I then realized that I shouldn't have moved the `index` subdirectory, so I moved that back to `/Volumes/SSD/Bitcoin/blocks/index`. Having an empty `blocks` dir with just and `index` subdir is a bit weird. Perhaps after @jimpo's #11857 is merged, we could just move / assume all indexes to be there (if `-blocksdir` is set)?

Worse, it created a directory `/Users/bitcoin/blocks/blocks`, which seems like a bug. I had to set `blocksdir=/Users/bitcoin` instead.
{
    if(!ECC_InitSanityCheck()) {
        InitError("Elliptic curve cryptography sanity check failure. Aborting.");
        return false;
    }
    if (!glibc_sanity_test() || !glibcxx_sanity_test())
        return false;
    if (!Random_SanityCheck()) {
        InitError("OS cryptographic RNG sanity check failure. Aborting.");
        return false;
    }
    return true;
}
static bool AppInitServers()
{
    RPCServer::OnStarted(&OnRPCStarted);
    RPCServer::OnStopped(&OnRPCStopped);
    if (!InitHTTPServer())
        return false;
    StartRPC();
    if (!StartHTTPRPC())
        return false;
    if (gArgs.GetBoolArg("-rest", DEFAULT_REST_ENABLE)) StartREST();
    StartHTTPServer();
    return true;
}
void InitParameterInteraction()