Are you using gmail accounts?
Yes, you need to have the .NET 5 runtime installed. If you don't have it, you will be asked to download it upon first opening of the Keylogger. If you have a 64-bit system, then that's the version you should download.
I can't seem to figure out why it doesn't work for you either.
All I can do is give you a few more things to try:
- make sure you have a 64bit system by pressing your windows key, then typing "System information"
- go to this link: https://dotnet.microsoft.com/download/dotnet/5.0/runtime , under "Run desktop apps" select "Download x64" and install this framework
- download the Keylogger once again (it's been updated)