Mobile experience on smaller screens 7. 1

I'm steadily updating my site, teaching myself code and css customisation as I go. I've been careful with the mobile design to ensure that everything fits and I've reduced the breakpoint to 641lpx to cater for smaller screens. 

When I asked for feedback on a page in a UK group I was shown that on this individual's Samsung phone there were overlaps with the sign up form in the footer and that the sign up form pop up also didn't fit (see screenshots). 

I added a space before the privacy statement and that altered things on the footer when I looked at it with my pixel 7 pro. She says hers didn't shift. 

Is this something that I can fix (without it all looking screwy on other sized screens), is it likely her settings and therefore a anomaly, or is it just something out of my sphere of control and not worry about it? 

Www.makers-and-menders.co.uk if anyone wants to check it themselves and compare.