Known issue unfortunately (as per link at bottom of https://forum.mx5oc.co.uk/t/nd-infotainment-screen-cracks/137159
There is a fix but it looks quite involved:
https://www.tylerwatt12.com/repair-guide-nd-mazda-mx-5-touchscreen-cracks-de-lamination/
Best bet is to replace the screen. If doing so, apparently later model screens have either a better contrast or resolution (or both, I can’t remember)