Do IB training programs in banks actually make you disconnect your mouse?

Not at my bank (BB). It improves efficiency most of the time, but my computer is so slow that sometimes it's faster to just use the mouse.

It's definitely way faster to use excel without a mouse (once you've acclimatised) in like 80% of scenarios (exceptions would be dialogue boxes and charts imo where it gets a bit awkward). It does take some getting used to and I don't think training is enough time to fully get used to it tbh. But e.g. something I do very often is set stuff as percentages and have to add/remove a decimal point. Way faster (and more fluid) to click alt h p and alt h 0 than to take my hands off the keyboard from typing, move to my mouse, click on % etc. On the ribbon.

If you have to use your mouse for basic ass excel, expect to be up until the crack of dawn

Definitely not. Even many years into banking I still use my mouse for a small handful of things. just habit at this point

The more keyboard shortcuts you use/know the better, really saves a significant amount of time. the quick access toolbar in both Excel and PPT will become your best friend.