Compatibility checker didn't identify VSTACK as an issue for Excel 2021

I have a pretty complex spreadsheet which I developed using my Office 365 subscription.  In it I used some pretty new functions including VSTACK.   I needed to share the spreadsheet with someone who has the Office 2021 home and student installed, but it didn't work for them.   After a lot of digging around I found that the problem was a VSTACK function I had used.   I wanted to find out if I had other instances of VSTACK and possibly other unsupported functions, so I ran the Excel compatibility checker with only the 2021 and 2023 versions selected.   It failed to identify any issues even though I was already aware that I had at least one function that the 2021 version doesn't support.   It looks like I'll have to use trial and error to find any other similar issues.