That is still an option, but there is a tradeoff. There is a button in the software to enable on-board memory mode.
You lose all your key assignment controls and fine-tuned DPI settings, but it stores on the device. If you want to have those features available, the mouse needs some software on the PC to talk to for more fine-grained control.
Ubisoft’s bean counters had some trouble reading the market on this one.
They left Steam because they felt the 30% cut that Valve takes for sales on their platform is way too high, but didn’t account that users of Steam are really entrenched into that platform and don’t want to leave just for the chance to play an Ubisoft title. So instead of seeing 70% of Steam sales of their games, they saw 0.