Hey,
i was rly long playing arround with Windows an Linux now. and i dont get it fully working at all!

Windows:
installed umod agent via Powershell

&powershell -NoProfile -ExecutionPolicy unrestricted -Command "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12;&([scriptblock]::Create((Invoke-WebRequest -UseBasicParsing 'https://umod.io/umod-develop.ps1')))"​

umod install valheim -P --filter=umod​

Object reference not set to an instance of an object. (uMod.Agent)
   at uMod.Agent.Commands.Install.InstallCore(GameInfo gameInfo, PackageManager packageManager, Lock versionLock, IWorkflowContext context) in /builds/umod/tools/agent/src/uMod.Agent/Commands/Install.cs:line 1119
   at uMod.Agent.Commands.Install.Handle() in /builds/umod/tools/agent/src/uMod.Agent/Commands/Install.cs:line 921
   at uMod.Agent.Commands.Command.Invoke() in /builds/umod/tools/agent/src/uMod.Agent/Commands/Command.cs:line 274
   at uMod.Agent.Service.HandleCommand(Command command) in /builds/umod/tools/agent/src/uMod.Agent/Service.cs:line 216
   at uMod.Agent.Service.HandleCommand(IEnumerable`1 args) in /builds/umod/tools/agent/src/uMod.Agent/Service.cs:line 278
   at uMod.Program.Main(String[] args) in /builds/umod/tools/agent/src/uMod/Program.cs:line 72
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at uMod.Agent.Commands.Install.InstallCore(GameInfo gameInfo, PackageManager packageManager, Lock versionLock, IWorkflowContext context) in /builds/umod/tools/agent/src/uMod.Agent/Commands/Install.cs:line 1119
   at uMod.Agent.Commands.Install.Handle() in /builds/umod/tools/agent/src/uMod.Agent/Commands/Install.cs:line 921
   at uMod.Agent.Commands.Command.Invoke() in /builds/umod/tools/agent/src/uMod.Agent/Commands/Command.cs:line 274
   at uMod.Agent.Service.HandleCommand(Command command) in /builds/umod/tools/agent/src/uMod.Agent/Service.cs:line 216
   at uMod.Agent.Service.HandleCommand(IEnumerable`1 args) in /builds/umod/tools/agent/src/uMod.Agent/Service.cs:line 278
   at uMod.Program.Main(String[] args) in /builds/umod/tools/agent/src/uMod/Program.cs:line 72​

[email protected]:~/valheim$ umod install valheim -P --filter=umod
Failed to extract Valheim in directory: /home/finest/valheim/valheim_server_Data/Managed
Access to the path '/System.Core.dll' is denied.
Core install failure
App update successful​

as root it was installing the umod valheim files in the / directory of my linux not in the folder dir iam

so it was looks like that

u need to

source ~/.profile​

this issue was fixed with the latest umod update thanks !