Thank you for your response. You mentioned that your file will change dates every day. I'd like to know, are we working on shared Excel files? If not, does the issue only occur on a specific file?
The default date format differs depending on the Region or location. This why it is best if you post this issue in the
Excel UserVoice.
Disclaimer:
A workaround that we have is for you to change the region on your Microsoft Account (e.g. English (United Kingdom). However, it will affect the PC and other Office apps, not just the Excel Online. If you want to continue and use the workaround, you may check
your inbox. I have sent you a private message providing a workaround on your concern. Kindly go to
Profile name > My Profile > View private messages.
Should you need any additional assistance regarding our scope of support, feel free to post your queries anytime.