@amrits, @alex.lange: I have some more information that may help scoping the problem. Actually the 780 MHz lock up only happens when restarting Cyberpunk with DLSS frame generation 4X mode activated. If it is set to 2X or 3X, and the game is restarted, then the boost works (2737 Hz). Does this help? Can other people with other games try to set DLSS 2X or 3X in settings?
EDIT: the plot thickens: it may happen during game in 3X after all. However, contrary to 4X, this does not happen immediately, but at some point during play, without reproducibility, as reported by @alex.lange. However with Cyberpunk, once it is locked to 780 MHz there is no coming back, even if settings reduce frame generation (or disabling it), until game is restarted. It is as if there was some throttling happening and then lock down to 780 MHz.