The pedals in a car always do the same thing every time you press them, in every car you get into. Mouse buttons are not like this. Different applications use them differently. There may be a sizeable chunk that are reasonably consistent but there are tons of outliers that do all kinds of bizarre stuff like using right click to select or to cancel an operation or to bring up a tool tip. Sometimes it’s left click to select and right click to move.

Plus you never know what’s going to be in a context menu until you right click to open it. Sometimes you move the mouse slightly and right click something else and get a different context menu. For an older person with declining vision this can be very confusing. Fixed menus at the top of the screen are discoverable. You can even search for what you want in the help menu. Context menus are not discoverable.

I’m glad your mother knows how to install video cards. My aunt worked at a TV factory installing boards into the case and soldering all the through-hole components to the board. She’s still pretty baffled by computers but she’s almost 80 years old and rarely needs them.

You have to be willfully ignorant or brain damaged to not understand how a 2-button mouse works after the first time using it. The context menu does different things depending on the context. Someone that can't understand that is seriously in trouble in life. It's not something that should be confusing at all.

And as I said, hopefully your father never visits any websites, because they are all different with information in different places on every website. The world must be an extremely frustrating and hostile place for someone that gets confused by a 2 button mouse. I honestly feel bad for your father if everything you say is true.