Compaq keyboard

I only just found this by Googling for "split space-bar" - (slightly edited
for my own reasons). It does work but as yet I haven't powered down to see
if it returns to the default "left = backspace" mode.

Spit Spacebar Fix - Compaq Keyboard:

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It is possible to change the functioning of the split space bar on a
Windows based computer. The default is that the right half of the bar
spaces, and the left half backspaces.

If you hold down the Control, Alt, and Shift keys simultaneously, and then
hit the left half of the bar twice it will toggle to a mode in which both
halves of the bar will space.

If you repeat this procedure, it will toggle to a mode in which the left
half of the bar will space and the right half will backspace (the reverse
of the default)

If you repeat this procedure a third time, you will return to the default.
Once you changed the functioning of the split bar, it will stay that way
until you change it again or until you shut down your computer. (You may
re-start the computer from the Shut Down menu without losing the changes;
it's only an actual shut-down that erases the changes.)