Не ну вроде даже работает :)

TransportCompany/TransportCompany/App.config

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <appSettings>
+    <add key="connectToDb" value="Host=192.168.56.101;Port=6000;Database=elegev;Username=elegev;Password=user"/>
+  </appSettings>
+</configuration>

TransportCompany/TransportCompanyDatabaseImplements/ElegevContext.cs

@@ -1,6 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.Configuration;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
+using Microsoft.Extensions.Options;
 using TransportCompanyDatabaseImplements.Models;
 
 namespace TransportCompanyDatabaseImplements;
@@ -26,9 +29,11 @@ public partial class ElegevContext : DbContext
 
     public virtual DbSet<TypeTransportation> TypeTransportations { get; set; }
 
+    string dbName = ConfigurationManager.AppSettings["connectToDb"];
+
     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
 #warning To protect potentially sensitive information in your connection string, you should move it out of source code. You can avoid scaffolding the connection string by using the Name= syntax to read it from configuration - see https://go.microsoft.com/fwlink/?linkid=2131148. For more guidance on storing connection strings, see http://go.microsoft.com/fwlink/?LinkId=723263.
-        => optionsBuilder.UseNpgsql("Host=192.168.56.101;Port=6000;Database=elegev;Username=elegev;Password=user");
+        => optionsBuilder.UseNpgsql(dbName);
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {

TransportCompany/TransportCompanyDatabaseImplements/TransportCompanyDatabaseImplements.csproj

@@ -16,6 +16,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="7.0.3" />
+    <PackageReference Include="System.Configuration.ConfigurationManager" Version="7.0.0" />
   </ItemGroup>
 
   <ItemGroup>