What to do with files that relate to multiple categories?

Hello, I have a bit of a problem with organizing the files that relate to multiple categories. Maybe I did the category splitting wrong, but I don’t know how else to do it cleanly.

For context, I teach 4 different topics, Python, C#, Unreal Engine, and 3D Modelling.
The structure I have for now is like this.

00-09 Meta
|- ...
10-19 Python
|- 11 Notes
|- 12 Topics
|- 13 Projects
|- 14 Resources
20-29 C#
|- 21 Notes
|- 22 Topics
|- 23 Projects
|- 24 Resources
30-39 3D
[Same as above]
40-49 Unreal
[Same as above]

The problem I’m facing is the resources folder. Often some resource is relevant to multiple groups. Like a model repository is relevant both to 3D and Unreal groups, or a video explaining inheritance is relevant both to C# and Python groups.
(Each resource is a text file with a link and some notes about it)

So this leaves either copying the file into multiple categories, which is sub-optimal. Making another category/area for every combination which will make finding the resource harder. Or having another area for resources split into categories they cover, which makes relating them to the classes more cumbersome.

But maybe I’m missing something, or thinking about it the wrong way, so I’d like to know if anyone has any ideas how to handle this?
(And feel free to critique the organization too, I’ve only just started with it, so reworking it is no big deal)

Answering my own question, but after thinking about it more, I think what I can do is have “Resources” as a separate category with every resource in it (maybe categorized in some way) and then for each group have a file that references them. That way I won’t have duplicates, and can still find relevant resources, although with an extra step.

So it can be like

50 - 51 [some area]
|- 51 Resources
  |- 51.01 Model sites
  |- 51.02 Python docs
  |- 51.03 Regex tester site

And then each group can have a “XX.01 Resources.txt” file that would reference the relevant resources.

Python resources
- 51.02 Docs
- 51.03 Regex tester

So basically combining two bad ideas into kinda decent one.

Still don’t 100% like it, so if anyone has something better, do share.

I think you’ve found the best solution, but here’s another option you can try if you want.

I’m not sure about Windows computers, but on a Mac you can drag a file from one place to another while holding the control and option keys and it will create an alias to that file in the new location. So you only have one file but multiple aliases to that file wherever else you need it.

I do this with whole folders. I have my car insurance folder under my insurance category, but I have an alias to that insurance folder in my Automotive category as well.