Bitcoin-qt data on external drive
It is trying to acquire a lock on the lockfile in the data directory, which likely fails due to not being supported on the network file system you use to access your NAS.

Even if that could be safely ignored (the lockfile is just there to prevent you from running multiple Bitcoin Core instances on the same directory), it is a warning that more problems exist. In general, running a database on a network filesystem is a bad idea because of lack of support for operations or guarantees that databases require. It would either just not work, be very slow, or get corrupted very easily.

However, this is all because of the databases used (blocks/ index/, chainstate/ and wallet.dat). The block data itself is not a database, and could be moved elsewhere. Bitcoin Core does currently not support moving just the block data elsewhere, though.