What’s the goal here? Learning C? Learning programming more generally? Sorting out the previous development work within (presumably) newer Xcode tooling? Something else?
I’m going to assume the goal here is learning to program in this reply, and that might not be your goal here.
Usual C “Hello World” starting point nowadays would be a (existing or new) Xcode project comprised of a command line tool template project written in C. Or command line.
For learning C from course materials not tailored to (recent) Xcode, consider opening a Terminal window and work there with an editor and the command line, at least to get the hang of the environment, and to be able follow most any UNIX- or Linux-focused Clang-based C programming guide. Thismapproach also avoids adding the scale and scope and complexity of Xcode into learning the language.
This assuming you’re learning about C and language-specific C I/O like printf and such, and not building an app with a graphical user interface (GUI)muser interface (UI) written in (probably) Objective C.
Apple is pushing Swift hard, and the tools all lean that way, including Xcode and Playgrounds app. If you’re learning to program on an Apple platform, then using Swift and Playgrounds and the available intro materials can be a way. (C is the deep end of the pool, when learning.)
For GUI interface development work, Apple has been pushing Swift and SwiftUI, though Swift and Objective C can both still use AppKit (Mac) or UIKit (devices).
Support for C, C++, Objective C, and such all still exist, as well.
Apple tries to position Swift as an introductory language, though it’s really not. It’s also been a moving target, which tends to make finding contemporaneous coursework and related materials more difficult. This includes the Xcode UI itself routinely getting reorganized, as you’ve discovered.
One of the more common choices for an introductory programming language is Python. Harvard has a free introduction to computing and to programming in Python, CS50p:
https://cs50.harvard.edu/python/
For folks just getting started and learning program flow and related topics, Scratch can also be useful. (Harvard intro.)
C, bluntly, is the deep end of the programming pool. It is closer to a high-level assembler than to any sort of modern programming language. (Note: I use C a whole lot.)
Apple Playgrounds app is probably the closest for introducing programming in the Apple language realm, and can be a good path for learning Swift — but there are big gaps in coverage past the Playgrounds introductory and Swift introductory materials, including algorithms and data structures, and a view toward how computers (and apps) are constructed such as what CS50P covers, or deeper into computer science and concepts with CS50x:
https://cs50.harvard.edu/x/
Some of the previous discussions on this and similar:
Where can I learn about Swift? - Apple Community
I'm just starting out coding/programming - Apple Community
Good places to learn swift for IOS app de… - Apple Community
Caveats, too: There’s a great big gap between the Apple intro materials and using the Xcode and related tooling and app designs, and an equally big gap from the introductory manuals and such to algorithms and data structures, and debugging, and UIs and the rest. And I’d be exceedingly cautious around using AI code generation and related tooling, as the introduced bugs in the (auto-completion-generated) code can be quite spectacular, or quite subtle.
