How do I reformat MY Passport (for PC) for use with both Mac and PC?

I re-formatted the drive with my MacBook Air to exFAT, which I understand supercedes FAT32. However, when I plug MY Passport into my Dell laptop, I receive an error message “t the disk in drive F is not formatted. Do you want to format now?”

I’m selecting no because I do not want to lose data.

Why is it asking me to reformat?