There is a note about a cuttable trace but I’m not sure what effect cutting it has?
RP2350 supports an external PSRAM chip, which requires a single CS line to select it. On PGA2350 we include 8MB of that RAM and wired its CS to GP47.
If you need that pin for any other purpose (such as the 8th ADC) and are okay with loosing PSRAM access, then there is a trace on the rear of the board that can be cut to disconnect CS from GP47.
And any comment on relevance of RP2350-E9 Erratum to using the ADC (from MicroPython/CircuitPython) would be great
It is still early days in understanding the behaviour of the RP2350 regarding this. Some discussion is happening here too: RP2350: Internal pull down issue
Hope that helps