cannot build dll, Feature 'global using directive' is not available in C# 7.3 or error CS0246: The type or namespace name 'BaseUnityPlugin' could not be found

[LJWxyz]

Below is my .csproj for dotnet --version
7.0.200

---

<TargetFramework>net7.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>

<PackageReference Include="Harmony" Version="0.3.0" />
<PackageReference Include="HarmonyX" Version="2.10.1" />
<PackageReference Include="Lib.Harmony" Version="2.2.2" />

	<Reference Include="0Harmony">
		<HintPath>C:\afolder\BepInEx\core\0Harmony.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="Assembly-CSharp">
		<HintPath>C:\afolder\Managed\Assembly-CSharp.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="Unity">
		<HintPath>C:\afolder\Managed\UnityEngine.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="UnityEngine.CoreModule">
		<HintPath>C:\afolder\Managed\UnityEngine.CoreModule.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="BepInEx.Unity">
		<HintPath>C:\afolder\BepInEx\core\BepInEx.Unity.Common.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="BepInEx">
		<HintPath>C:\afolder\BepInEx\core\BepInEx.Core.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="BepInEx.Core.Mono">
		<HintPath>C:\afolder\BepInEx\core\BepInEx.Core.Mono.dll</HintPath>
		<Private>False</Private>
	</Reference>
	<Reference Include="Mono">
		<HintPath>C:\afolder\BepInEx\core\Mono.Cecil.dll</HintPath>
		<Private>False</Private>
	</Reference>

---

Anything wrong with the setup?Any dll(s) in managed is from the game and BEPIN is for bepin or harmony stuff.
errors for dotnet7.0

Package 'Harmony 0.3.0' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8' instead of the project target framework '.NETCoreApp,Version=v3.1'. This package may not be fully compatible with your project.
\Class1.cs(13,23): error CS0246: The type or namespace name 'BaseUnityPlugin' could not be found (are you missing a using directive or an assembly reference?)

I tried using dotnet3.1,and target net framework 4.8 but i get no dll out,after installing 4.8 and building it>

Build succeeded.

D:\2ndProgramFiles\insec\DOTNETcompiler\dotnet3_1\sdk\3.1.426\NuGet.targets(128,5): warning : Unable to find a project to restore!
1 Warning(s)

dir /b
MyProject
net3_1proj
net7proj
TestmodMBMtest2.sln

\MyProject>dir /b
Class1.cs
MyProject.csproj

my cs code has these deps>
using System;

using BepInEx;
using BepInEx.Unity;

using HarmonyLib;

what do i need to do to check or debug?