> The problem is that I can't get 5V on the A1 line, it stays low
> no matter what

You haven't busted the pin have you ? I'd have thought there'd
be the danger of the button being pressed while A1 is high and
an output and exceeding the output mA capability. A limiting
resistor would be a good idea, anything > 5000/20 ohms. It
seems to me that A1 should be an input and pulled high. Forcing
an output low by grounding doesn't sound right or sensible, unless
I'm really misunderstanding that diagram. Which I notice appears
to be the only hand-drawn diagram at the site. Untested ?

You could adapt a bistable, using the P-ch FET as the high-side
load

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