A:Answer Yes, the Dell S2725QC supports DisplayPort Alt Mode over USB‑C, however your proposed cable (DP → USB‑C Display) will not work. A DisplayPort output on your graphics card is not capable of generating USB‑C DP Alt Mode signaling.
DP Alt Mode is not passive
It requires:
A USB‑C controller,
USB‑C lane negotiation (CC pins, power role detection),
A plain DP port cannot do this, even DP 2.1.
Option A — Use HDMI 2.1 (Best for desktops). Option B — USB‑A + HDMI combo (if you want USB hub). Option C — Only if your GPU has native USB‑C.