Upgrade from 4.5.3 to 5.4.3

Hello,
I have been trying to upgrade one of our PSU environments to 5.4.3 from 4.5.3 but keep getting errors when trying to relaunch the service post upgrade. I have upgraded the database to sqlite.
been trying to sift through the forums but i can’t seem to find anything useful. hopefully someone can help

I get below in the log file when trying to execute the service:
[INF] Using database connection string:
[FTL] Fatal error starting PowerShell Universal.
System.ArgumentNullException: Value cannot be null. (Parameter ‘s’)
at System.ArgumentNullException.Throw(String paramName)
at System.Text.Encoding.GetBytes(String s)
at Universal.Server.Startup.ConfigureServices(IServiceCollection services) in D:\a\universal\universal\src\Universal.Server\Startup.cs:line 271
at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
at System.Reflection.MethodBaseInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs, BindingFlags invokeAttr)
at System.Reflection.MethodBaseInvoker.InvokeWithOneArg(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture)
at Microsoft.AspNetCore.Hosting.ConfigureServicesBuilder.InvokeCore(Object instance, IServiceCollection services)
at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.UseStartup(Type startupType, HostBuilderContext context, IServiceCollection services, Object instance)
at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass7_0.b__0(HostBuilderContext context, IServiceCollection services)
at Microsoft.Extensions.Hosting.HostBuilder.InitializeServiceProvider()
at Microsoft.Extensions.Hosting.HostBuilder.Build()
at Universal.Server.Program.Main(String args) in D:\a\universal\universal\src\Universal.Server\Program.cs:line 37