Hi Tom,
Welcome to community forum. It’s my pleasure to assist you.
According to your description, we tested at our end and we couldn’t reproduce this issue. In our test, we type the data as you provided in Excel online and set its format as General and then click open in desktop. We didn’t meet the scenario as you
mentioned, it still turns out to be the same as the online version. And both of the formats in online and desktop are General.



In this way, we would like to confirm with you about the format at your end, or you could also change its format to date. (When we set date as format, we couldn’t reproduce this issue either)
If the issue still exists after changing the format, would you mind providing the following information to help us narrow down the issue?
1.Your Office subscription screenshot via File>Account>Product Information. In order to protect your privacy, please help us mask your PII, such as email address.
- May we know your cell format on both online and desktop app?
- Will this issue only happen to the specific workbook? If so, could you please upload it to OneDrive and then share the link in public? So that we could test at our end and share the test result as soon as possible. Please note that don’t upload
files included private content. Reference:
Upload
and save files and folders to OneDrive
Share OneDrive files and folders
Wish you have a good day.
Best Regards,
Sandro