Ideas for basic C# projects

If you want to do backend development I would suggest focusing on that. You will need to learn how to interact with a database, so following the EF Core tutorial should be helpful. For web development you have the blazor tutorial, while this also covers frontend development, you cannot really avoid learning some kind of frontend development. An alternative would be to create a webAPI project and write a separate console application to call that API.

After you have learned the basics I would suggest writing a simple messaging/blog application. This should teach you how to connect the web application to the database. You can then start adding any new features you can think of. Take a look at similar applications if you want ideas for features.

A calculator is a good start you can make as complex as you want. Both command line, and GUI when you want to.

It sounds like you're getting started with programming; congrats! Welcome to the club! One of my favorite projects to do when I started learning C was a program that allowed you to search recursively for a word in a directory of files. I went on to add (limited) regex support, parallelization, etc. It sounds like a simple task (process arguments, list files in a directory, iterate through the files, search for the word), but it helped me get out of the tutorial/documentation stage. It's also a great way of learning the C# (or in my case, C) way of doing things.

If that isn't really interesting for you, I would recommend you just find a cool program and see if you can replicate it. Again, I'd recommend starting with command line utilities, and move on to projects that might be more in your wheelhouse: make a simple key-value database, try implementing an HTTP server, or make a static site generator.

It's ok if you bite off a bit more than you can chew. See how far you can get, and then come back later.

Make a Minecraft clone. Then add whatever blocks you want.

What sorts of things interest you? Can you build something related to your hobbies, or a tool that helps you automate some boring, time consuming task?