US dates entered suddenly being interpreted as European dates

I have a worksheet I use to calculate my volunteer mileage for tax purposes, copying it each year to a new version for the current year. I enter in the date in the first column (mm/dd/yy) and it displays in my desired format (mm-dd-yyyy). Worked great for years... until today. I cleared out the data and started entering in dates, and I noticed some of the dates were changing to the correct format and others were staying in the entered format. Upon further investigation, I realized the entered dates were being interpreted as European dates (dd/mm/yy). I changed the formatting for the column to mmm-dd-yyyy and saw this plainly.

I confirmed that the Windows regional attributes were correctly set for the US, including the date formats. (I've never touch this, but I wanted to be sure.) I went back and recopied the original worksheet to the new year's version, and I noticed all of the dates in both the old year's and new were now being shown in the dd-mm-yyyy format. When I entered in 1/6/25, and it displayed as Jun-01-2025. What the heck? I am baffled as to why this is suddenly happening for a worksheet that has been performing perfectly fine for several years.

Thoughts?