Hi Donald,
Thanks for reaching out. This seems to be a known issue introduced in the latest Excel Beta build 16.104, where checkboxes no longer render visually, even though their state is still detectable when hovering over the cell.
First, try restarting Excel and your device to rule out any temporary rendering glitches.
Second, check if hardware graphics acceleration is causing the issue. In Excel, go to File > Options > Advanced > Display, then enable “Disable hardware graphics acceleration”, and restart Excel.
Third, if the issue persists, consider rolling back to a previous beta build or switching to the Current Channel until a fix is released. You can do this via the Office Deployment Tool or by adjusting your update channel settings through Group Policy or the Office Insider settings.
Lastly, I recommend reporting this directly through Help > Feedback > I have a suggestion in Excel, so the product team is aware and can prioritize a fix.
If this helps, please mark the answer as accepted so others can find it too.
Best,
Carl