Хотелось бы стать специалистом по backend, а не fullstack.
Так не получится, либо очень мало вероятно.
большинство вакансий по c# это идет fullstack разработка и активная работа с фронтом
Если брать back-end, тогда да. Если брать desktop, то там ситуация другая.
Если хотите работать на веб, тогда вот вам с чего начать (Чисто ключевые моменты для изучения asp.net core MVC):
Client:
1. Html/css
1.1 margin, padding
1.2 !important
1.3 class
1.4 :hover, :active, :focus-visible
1.5 media requests
2. Bootstrap 5
2.1 form-control
2.2 alert, alert-danger
2.3 d-none
2.4 row, col-sm, col-md, col-lg
3. Java Script
3.1 let, dynamic object
3.2 document
3.3 getElementById
3.4 getElementBySelector
3.5 innerHtml
3.6 undefined
3.7 addEventListener()
3.8 JSON
3.9 JSON.stringify()
3.10 JSON.parse()
4 jQuery
4.1 jQuery selectors
4.2 .on()
4.3 .on('click', ... )
4.4 .change()
5 ajax
5.1 ajax HttpGet request
5.2 ajax HttpPost request
5.3 ajax send FormData
Simple C#:
6 OOP
6.1 Data types
6.2 Condition operators (if-else, switch). bool type
6.3 Loops (while, do-while, for, foreach)
6.4 array
6.5 List<>
Classes in C#
7.1 Classes
7.2 Fields
7.3 Properties
7.4 Constructors
7.5 Methods
7.6 Inheritance
7.7 Abstract classes
7.8 Abstract and virtual methods
7.9 Interfaces
7.10 Generics
7.11 Generic Methods
7.12 Generic Interfaces
7.13 Principals of OOP
Server (asp.net):
8.1 MVC architecture in asp.net
8.2 Controllers and Actions
8.3 Routing
8.4 [HttpGet]. [HttpPost]
8.5 [IgnoreAntyforgeryToken]
8.6 IActionResult
8.7 Razor Pages
8.8 Build correct model in asp.net mvc
8.9 View
8.10 Dependency Injections
8.11 asp.net mvc configuration
8.12 AddSingleton, AddScoped, AddTransient
Entity Framework
9.1 DbContext
9.2 DbSet<>
9.3 Connection String Parameters
9.4 IEntityTypeConfigraiton<>
9.5 EF Core one-to-one configuration
9.6 EF Core one-to-many configuration
9.7 EF Core many-to-many configuratio
9.8 .Include()
9.9 Migrations, Database.Migrate()
9.10 asp.net core .AddDbContext()
9.11 Generic Repository Antipattern
9.12 How to build custom services and include them to Dependency Injection
10. Fluent Validation in asp.net mvc
11. Authentication/Authorization
11.1 Different between Authentication and Authorization
11.2 Cookie
11.3 JWT (JSON web token)
11.4 Register authentication (app.UseAuthentication, app.UseAuthorization)
11.5 Claims (Claim, ClaimPlincipal, ClaimIdentity)
11.6 Authentication By Cookie
11.7 services.AddAuthentication()
