I’m pretty sure you’ll just have to cut it out of a rectangle in another program like gimp, sorry.

If you just want to do it for the fuck of it look at how old simple filesystems like FAT12 work and implement them in whatever high-level programming language you’re most comfortable, maybe with FUSE as others have suggested since there are beginner-level tutorials for that.

it’s actually better than some of my modern code because it’s not LLM-ified to save time.

Hmm that seems like an indication you’re rushing things and maybe ought not do that?? 🤦