The best 4K Remux looks identical to the physical disc. You lose nothing. But you also gain nothing—no upscaling, no sharpening, no "AI enhancement."
The term "REMUX" is short for "Remultiplex." To understand it, one must first understand the structure of a commercial Blu-ray disc. A movie on a disc is not a single file; it is a collection of streams (video, audio tracks in various languages, and subtitle files) packaged together in a container format (usually .MKV or .M2TS ).
Moreover, it restores agency. In a streaming world where your "watchlist" is algorithmically curated, a local REMUX library is a deliberate, personal archive. It is a statement that some experiences are too important to be left to the mercy of an internet connection.