Yes, the Canon EOS R5 Mark II works with the Sony SF-G Tough 128GB — with conditions (see below).
Sony SF-G Tough writes at 299 MB/s. Canon R5 Mark II SD slot supports 4K30 at lower bitrates — 299 MB/s meets that floor. 4K60 and above requires CFexpress Type B in the primary slot; SF-G Tough cannot sustain those rates in the SD slot.
Conditions for compatibility
4K30 via SD slot supported. 4K60 and above requires CFexpress Type B slot — SD slot speed insufficient for high-framerate modes.
“Canon EOS R5 Mark II Compatible Cards: SD slot accepts UHS-II and UHS-I; for movie recording use a card with ample performance for the movie recording quality per Canon online manual.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)