I had the same issue. As well as an "Unknown Publisher" warning from Windows Defender.
Previously I used the installer for HeidiSQL 9, and it installed the 64 bit version to
Running the HeidiSQL 10.0.0.5460 installer, after closing the running HeidiSQL 9 x64, did not replace the executable at
C:\Program Files\HeidiSQL\heidisql.exe but installed to
I also tried the HeidiSQL 10.0.0.5461 installer with the same results.
See attached image
Take note of the name of the executable properties dialog