Choose the Font color as Red.
Go to the Background tab and choose a red background if you want the cells to flash red as well.
???
Or maybe that's after a macro is added? That part of the info. that came up seems a bit contradictory. Not that it's a big deal, as I alluded to above.
Go to ChatGPT and ask it. It is so user-friendly I often forget that it isn’t a person.