The most likely explanation is that since LPDDR5x is backwards compatible with LPDDR5, Samsung chose to use it with the Snapdragon 6 Gen 3. The nuance here is that the LPDDR5x will operate at LPDDR5 speeds because that's the maximum bandwidth the CPU supports. The only advantage will be lower power consumption, nothing else.
For example, you can use a DDR4 3200 MT/s stick with a CPU that supports a max of say, 2666 MT/s... the stick will run at the lower speed, doesn't mean it can't be used or is a scam.
Its not really "no use", you see... you'll see slightly better power efficiency. One can argue that the difference is too small to notice, but that's also true for performance. Most users won't see the difference between LPDDR5 and LPDDR5x...
