delete the entire trainer manager and redownload it the new update requires you to redownload the trainer manager
one of the .NET could be damaged, re-install them to repair.
Have both these .NET CORE and FRAMEWORK Installed from Microsoft.
.NET Core 3.1 Desktop Runtime x86 Link
.NET Core 3.1 Desktop Runtime x64 Link
.NET Core Current Runtime x86 Link
.NET Core Current Runtime x64 Link
.NET Framework (get latest) Link
(Both x86 and x64 of the .Net Core MUST be installed)
Reboot PC when done.