Maybe this helps: People hire you to solve their problems. And they usually have relatively unique ideas, so they need someone who is able to realise those ideas. If the solutions were already available on the internet, they would just takes those solutions instead of hiring somebody. If some random tutorial could teach them the relevant knowledge, they would either hire somebody for minimum wage (at best) or they would do it themselves.
With this in mind, try to figure out what problems people might encounter when developing a 2D isometric game. The best way is to create your own little game and to realise your own ideas because, as aforementioned, you are expected to solve problems. At some point, tutorials won’t help you anymore anyway because the problems are too specific or too advanced.
Since you mentioned “2D isometric”, I’d like to point out that “2D isometric” is just the visualisation. I do not know what your potential employer is expecting from you but, if possible, don’t try to be a jack of all trades. If you are responsible for the tech art, learn shader programming. If you are responsible for translating the game designer’s idea into code, learn how to do that. Of course, this is just my personal opinion but if you dive into the two fields, you’ll notice that there is a lot to learn, and it could take years to become good in one of those fields. For this reason, it is better to mainly focus on one field.
Last but not least, if you intend to code things, learn C# in a more general context (if you haven’t already) to gain a better understanding of the programming language and programming in general. If you are interested in a free C# course, I can recommend Bob Tabor’s.
Good luck!
TLDR; Figure out what problems your future employers expects you to solve for them, and learn how to solve some of those problems. If you are not applying for a specific position, try to solve the problems in your own “2D isometric” game because those are very likely the same or similar problems as those you will encounter in the job.