Why All three listed modes send discrete data bits rather than an analog voice or image waveform, so all qualify as digital. Packet radio breaks data into addressed frames (usually AX.25) sent over the air, IEEE 802.11 is the WiFi standard that hams can run at higher power on overlapping 2.4 GHz and 5 GHz amateur allocations (as in Broadband-Hamnet mesh networks), and FT8 is one of the WSJT-X weak-signal modes that encodes short structured messages for decoding below the noise floor.
Watch out Each single-mode choice looks right on its own, which is the trap: the question asks which is a digital mode, not which is the only one, and none of the three is analog.
Packets, WiFi, FT8: all bits, no analog. When every choice moves data, pick 'all of these.'